Angualr JS Interview Questions and Answers

Q1. What is AngularJS?

Ans. AngularJS is an open-source JavaScript framework developed by Google. It helps you to create single-page applications or one-page web applications that only require HTML, CSS, and JavaScript on the client side. It is based on MV-* pattern and allow you to build well structured, easily testable, and maintainable front-end applications.

AngularJS has changed the way to web development. It is not based on jQuery to perform its operations. In spite of using ASP.NET Web form, ASP.NET MVC, PHP, JSP, Ruby on Rails for web development, you can do your complete web development by using most powerful and adaptive JavaScript Framework AngularJS. There is no doubt, JavaScript frameworks like AngularJS, Ember etc. are the future of web development.

Q2. Why to use AngularJS?

Ans. There are following reasons to choose AngularJS as a web development framework:

  1. It is based on MVC pattern which helps you to organize your web apps or web application properly.
  2. It extends HTML by attaching directives to your HTML markup with new attributes or tags and expressions in order to define very powerful templates.
  3. It also allows you to create your own directives, making reusable components that fill your needs and abstract your DOM manipulation logic.
  4. It supports two-way data binding i.e. connects your HTML (views) to your JavaScript objects (models) seamlessly. In this way any change in model will update the view and vice versa without any DOM manipulation or event handling.
  5. It encapsulates the behaviour of your application in controllers which are instantiated with the help of dependency injection.
  6. It supports services that can be injected into your controllers to use some utility code to fulfil your need.
  7. For example, it provides $http service to communicate with REST service.
  8. It supports dependency injection which helps you to test your angular app code very easily.
  9. Also, AngularJS is mature community to help you. It has widely support over the internet.

Q3. Why this project is called “AngularJS”?

Ans. Html has angle brackets i.e. <,> and ng sound like Angular. That’s why it is called AngularJS.

Q4. What are the advantages of AngularJS?

Ans. There are following advantages of AngularJS:

  • Data Binding – AngularJS provides a powerful data binding mechanism to bind data to HTML elements by using scope.
  • Customize & Extensible – AngularJS is customized and extensible as per you requirement. You can create your own custom components like directives, services etc.
  • Code Reusability – AngularJS allows you to write code which can be reused. For example custom directive which you can reuse.
  • Support – AngularJS is mature community to help you. It has widely support over the internet. Also, AngularJS is supported by Google which gives it an advantage.
  • Compatibility – AngularJS is based on JavaScript which makes it easier to integrate with any other JavaScript library and runnable on browsers like IE, Opera, FF, Safari, Chrome etc.
  • Testing – AngularJS is designed to be testable so that you can test your AngularJS app components as easy as possible. It has dependency injection at its core, which makes it easy to test.

Q5. How AngularJS is different from other JavaScript Framework?

Ans. Today, AngularJS is the most popular and dominant JavaScript framework for professional web development. It is well suited for small, large and any sized web app and web application.

AngularJS is different from other JavaScript framework in following ways:

  1. AngularJS mark-up lives in the DOM.
  2. AngularJS uses plain old JavaScript objects (POJO).
  3. AngularJS is leverages with Dependency Injection.

Q6. What IDEs you can use for AngularJS development?

Ans. AngularJS development can be done with the help of following IDEs:

  1. Visual Studio 2012, 2013, 2015 or higher
  2. Eclipse
  3. WebStorm
  4. Sublime Text
  5. TextMate

Q7. Does AngularJS has dependency on jQuery?

Ans. AngularJS has no dependency on jQuery library. But it can be used with jQuery library.

Q8. How to use jQuery with AngularJS?

Ans. By default AngularJS use jQLite which is the subset of jQuery. If you want to use jQuery then simply load the jQuery library before loading the AngularJS. By doing so, Angular will skip jQLite and will started to use jQuery library.

Q9. Compare the features of AngularJS and jQuery?

Ans. The comparison of AngularJS and jQuery features are given below:

Features jQuery AngularJS
Abstract The DOM Y Y
Animation Support Y Y
AJAX/JSONP Y Y
Cross Module Communication Y Y
Deferred Promises Y Y
Form Validation N Y
Integration Test Runner N Y
Unit Test Runner Y Y
Localization N Y
MVC Pattern N Y
Template N Y
Two-way Binding N Y
One-way Binding N Y
Dependency Injection N Y
Routing N Y
Restful API N Y

Q10. What is jQLite or jQuery lite?

Ans. jQLite is a subset of jQuery that is built directly into AngularJS. jQLite provides you all the useful features of jQuery. In fact it provides you limited features or functions of jQuery.

Here is a table of supported jQuery methods by jQLite.

jQuery Method Limitation, if any
addClass()
after()
append()
attr()
bind() Does not support namespace, selectors and eventData
Children Does not support selectors
clone()
contents()
css()
data()
detach()
empty()
eq()
find() Limited to lookups by tag name
hasClass()
html()
text() Does not support selectors
on() Does not support namespace, selectors and eventData
off() Does not support namespace, selectors
one() Does not support namespace, selectors
parent() Does not support selectors
prepend()
Prop
ready()
Remove
removeAttr()
removeClass()
removeData()
replaceWith()
toggleClass()
triggerHandler() Passes a dummy event object to handlers
unbind() Does not support namespace
val()
wrap()

Q11. Is AngularJS a library, framework, plugin or a browser extension?

Ans. AngularJS is a first class JavaScript framework which allows you to build well structured, easily testable, and maintainable front-end applications. It is not a library since library provides you limited functionality or has dependencies to other libraries.

It is not a plugin or browser extension since it is based on JavaScript and compatible with both desktop and mobile browsers.

Q12. What browsers AngularJS support?

Ans.The latest version of AngularJS 1.3 support Safari, Chrome, Firefox, Opera 15+, IE9+ and mobile browsers (Android, Chrome Mobile, iOS Safari, Opera Mobile).

AngularJS 1.3 has dropped support for IE8 but AngularJS 1.2 will continue to support IE8.

Q13. What is the size of angular.js file?

Ans. The size of the compressed and minified file is < 36KB. Q14. What are AngularJS features?

Ans. The features of AngularJS are listed below:

  1. Modules
  2. Directives
  3. Templates
  4. Scope
  5. Expressions
  6. Data Binding
  7. MVC (Model, View & Controller)
  8. Validations
  9. Filters
  10. Services
  11. Routing
  12. Dependency Injection
  13. Testing

Q15. How AngularJS handle the security?

Ans. AngularJS provide following built-in protection from basic security holes:

  1. Prevent HTML injection attacks.
  2. Prevent Cross-Site-Scripting (CSS) attacks.
  3. Prevent XSRF protection for server side communication.

Also, AngularJS is designed to be compatible with other security measures like Content Security Policy (CSP), HTTPS (SSL/TLS) and server-side authentication and authorization that greatly reduce the possible attacks.

 Q16. What components can be defined within AngularJS modules?

Ans. You can define following components with in your angular module:

  1. Directive
  2. Filter
  3. Controller
  4. Factory
  5. Service
  6. Provider
  7. Value
  8. Config settings and Routes

Q17. What is core module in AngularJS?

Ans. ng is the core module in angular. This module is loaded by default when an angular app is started. This module provides the essential components for your angular app like directives, services/factories, filters, global APIs and testing components.

Q18. How angular modules load the dependencies?

Ans. An angular module use configuration and run blocks to inject dependencies (like providers, services and constants) which get applied to the angular app during the bootstrap process.

Q19. What is difference between config() and run() method in AngularJS?

Ans. Configuration block – This block is executed during the provider registration and configuration phase. Only providers and constants can be injected into configuration blocks. This block is used to inject module wise configuration settings to prevent accidental instantiation of services before they have been fully configured. This block is created using config() method.

angular.module(‘myModule’, []).

config(function (injectables) { // provider-injector

  • This is an example of config block.
  • You can have as many of these as you want.
  • You can only inject Providers (not instances)
  • into config blocks.

}).

run(function (injectables) { // instance-injector

  • This is an example of a run block.
  • You can have as many of these as you want.
  • You can only inject instances (not Providers)
  • into run blocks

});

Run block – This block is executed after the configuration block. It is used to inject instances and constants. This block is created using run() method. This method is like as main method in C or C++.

The run block is a great place to put event handlers that need to be executed at the root level for the application.

For example, authentication handlers.

Q20. When dependent modules of a module are loaded?

Ans. A module might have dependencies on other modules. The dependent modules are loaded by angular before the requiring module is loaded.

In other words the configuration blocks of the dependent modules execute before the configuration blocks of the requiring module. The same is true for the run blocks. Each module can only be loaded once, even if multiple other modules require it.

Q21. What is Global API?

Ans. Global API provides you global functions to perform common JavaScript tasks such as comparing objects, deep copying, iterating through objects, and converting JSON data etc. All global functions can be accessed by using the angular object. The list of global functions is given below:

Name Description
angular.lowercase Converts the specified string to lowercase.
angular.uppercase Converts the specified string to uppercase.
angular.forEach Invokes the iterator function once for each item in obj collection, which can be
either an object or an array.
angular.isUndefined Determines if a reference is undefined.
angular.isDefined Determines if a reference is defined.
angular.isObject Determines if a reference is an Object.
angular.isString Determines if a reference is a String.
angular.isNumber Determines if a reference is a Number.
angular.isDate Determines if a value is a date.
angular.isArray Determines if a reference is an Array.
angular.isFunction Determines if a reference is a Function.
angular.isElement Determines if a reference is a DOM element (or wrapped jQuery element).
angular.copy Creates a deep copy of source, which should be an object or an array.
angular.equals Determines if two objects or two values are equivalent. Supports value types,
regular expressions, arrays and objects.
angular.bind Returns a function which calls function fn bound to self
angular.toJson Serializes input into a JSON-formatted string. Properties with leading $$
characters will be stripped since angular uses this notation internally.
angular.fromJson Deserializes a JSON string.
angular.bootstrap Use this function to manually start up angular application.
angular.reloadWithDebugInfo Use this function to reload the current application with debug information turned
on.
angular.injector Creates an injector object that can be used for retrieving services as well as for
dependency injection
angular.element Wraps a raw DOM element or HTML string as a jQuery element.
angular.module Used for creating, registering and retrieving Angular modules.

Q22. What is Angular Prefixes $ and $$?

Ans. To prevent accidental name collisions with your code, Angular prefixes names of public objects with $ and names of private objects with $$. So, do not use the $ or $$ prefix in your code.

Q23. What are Filters in AngularJS?

Ans. Filters are used to format data before displaying it to the user. They can be used in view templates, controllers, services and directives. There are some built-in filters provided by AngularJS like as Currency, Date, Number, OrderBy, Lowercase, Uppercase etc. You can also create your own filters.

Filter Syntax

{{ expression | filter}}

Filter Example

Q24. What are Expressions in AngularJS?

Ans. AngularJS expressions are much like JavaScript expressions, placed inside HTML templates by using double braces such as: {{expression}}. AngularJS evaluates expressions and then dynamically adds the result to a web page. Like JavaScript expressions, they can contain literals, operators, and variables.

There are some valid AngularJS expressions:

  • {{ 1 + 2 }}
  • {{ x + y }}
  • {{ x == y }}
  • {{ x = 2 }}
  • {{ user.Id }}

Q25. How AngularJS expressions are different from the JavaScript expressions?

Ans. AngularJS expressions are much like JavaScript expressions but they are different from JavaScript expressions in the following ways:

  1. Angular expressions can be added inside the HTML templates.
  2. Angular expressions doesn’t support control flow statements (conditionals, loops, or exceptions).
  3. Angular expressions support filters to format data before displaying it.

Q26. What are Directives in AngularJS?

Ans. AngularJS directives are a combination of AngularJS template markups (HTML attributes or elements, or CSS classes) and supporting JavaScript code. The JavaScript directive code defines the template data and behaviors of the HTML elements.

AngularJS directives are used to extend the HTML vocabulary i.e. they decorate html elements with new behaviors and help to manipulate html elements attributes in interesting way.

There are some built-in directives provided by AngularJS like as ng-app, ng-controller, ng-repeat, ng-model etc.

Q27. What is the role of ng-app, ng-init and ng-model directives?

Ans. The main role of these directives is explained as:

  • ng-app – Initialize the angular app.
  • ng-init – Initialize the angular app data.
  • ng-model – Bind the html elements like input, select, text area to angular app model.

Q28. How to create custom directives in AngularJS?

Ans. You can create your own custom directive by using following syntax:

var app = angular.module(‘app’, []);

//creating custom directive syntax

app.directive(“myDir”, function () {

return {

restrict: “E”, //define directive type like E = element, A = attribute, C = class, M = comment

scope: { //create a new child scope or an isolate scope

title: ‘@’ //@ reads the attribute value,

//= provides two-way binding,

//& works with functions

},

template: “

{{ myName }}

“,// define HTML markup

templateUrl: ‘mytemplate.html’, //path to the template, used by the directive

replace: true | false, // replace original markup with template yes/no

transclude: true | false, // copy original HTML content yes/no

controller: function (scope) { //define controller, associated with the directive template

//TODO:

},

link: function (scope, element, attrs, controller) {//define function, used for DOM manipulation

//TODO:

}

}

});

Q29. What are different ways to invoke a directive?

Ans. There are four methods to invoke a directive in your angular app which are equivalent.

Method Syntax
As an attribute
As a class
As an element
As a comment

Q30. What is restrict option in directive?

Ans. The restrict option in angular directive, is used to specify how a directive will be invoked in your angular app i.e. as an attribute, class, element or comment.

There are four valid options for restrict:

‘A’ (Attribute)-

‘C’ (Class)- ‘E’ (Element)-

‘M’ (Comment)-

Q31. Can you define multiple restrict options on a directive?

Ans. You can also specify multiple restrict options to support more than one methods of directive invocation as an element or an attribute. Make sure all are specified in the restrict keyword as:

restrict: ‘EA’

Q32. What is auto bootstrap process in AngularJS?

OR

How AngularJS is initialized automatically?

Ans. Angular initializes automatically upon DOMContentLoaded event or when the angular.js script is downloaded to the browser and the document.readyState is set to complete. At this point AngularJS looks for the

ng-app directive which is the root of angular app compilation and tells about AngularJS part within DOM. When the ng-app directive is found then Angular will:

  1. Load the module associated with the directive.
  2. Create the application injector.
  3. Compile the DOM starting from the ng-approot element.

This process is called auto-bootstrapping.

Example

Hello {{msg}}!

Q33. What is manual bootstrap process in AngularJS?

OR

How AngularJS is initialized manually?

Ans. You can manually initialized your angular app by using angular.bootstrap() function. This function takes the modules as parameters and should be called within angular.element(document).ready() function. The angular.element(document).ready() function is fired when the DOM is ready for manipulation.

Example

Hello {{msg}}!

‘undefined’=== typeof _trfq || (window._trfq = []);’undefined’=== typeof _trfd && (window._trfd=[]),_trfd.push({‘tccl.baseHost’:’secureserver.net’}),_trfd.push({‘ap’:’cpsh’},{‘server’:’p3plcpnl0783′}) // Monitoring performance to make your website faster. If you want to opt-out, please contact web hosting support.

Note

  • You should not use the ng-appdirective when manually bootstrapping your app.
  • You should not mix up the automatic and manual way of bootstrapping your app.
  • Define modules, controller, services etc. before manually bootstrapping your app as defined in above example.

Q34. How to bootstrap your angular app for multiple modules?

Ans. AngularJS is automatically initialized for one module. But sometimes, it is required to bootstrap for multiple modules and it can be achieved by using two methods:

  1. Automatic bootstrap (by combining multiple modules into one module) – You can combine multiple modules into single modules and your angular app will be automatically initialized for newly created module and other modules will act as dependent modules for newly created module.

For example, suppose you have two modules: module1 and model2, and you have to initialize your app automatically based on these two modules then you achieve this following way:

MULTIPLE MODULES BOOTSTRAP

{{name}}

{{name}}

  1. Manual bootstrap – You can manually bootstrap your app by using bootstrap()function, for multiple modules.

The above example can be rewritten as for manual bootstrap process as given below:

MULTIPLE MODULES BOOTSTRAP

{{name}}

{{name}}

{{name}}

Q35. What is scope in AngularJS?

Ans. Scope is a JavaScript object that refers to the application model. It acts as a context for evaluating angular expressions. Basically, it acts as glue between controller and view.

Scopes are hierarchical in nature and follow the DOM structure of your AngularJS app. AngularJS has two scope objects: $rootScope and $scope.

Q36. What is scope hierarchy?

OR

What is scope inheritance?

Ans. The $scope object used by views in AngularJS are organized into a hierarchy. There is a root scope, and the $rootScope can has one or more child scopes. Each controller has its own $scope (which is a child of the $rootScope), so whatever variables you create on $scope within controller, these variables are accessible by the view based on this controller.

For example, suppose you have two controllers: ParentController and ChildController as given below:

Manager Name {{managerName}}
Company Name {{companyName}}
Team Lead Name {{ teamLeadName }}
Reporting To {{managerName}}
Company Name {{companyName}}
Child Controller
Parent Controller

Output

Q37. What is the difference between $scope and scope?

Ans. The module factory methods like controller, directive, factory, filter, service, animationconfig and run receive arguments through dependency injection (DI). In case of DI, you inject the scope object with the dollar prefix i.e. $scope. The reason is the injected arguments must match to the names of injectable objects followed by dollar ($) prefix.

For example, you can inject the scope and element objects into a controller as given below:

module.controller(‘MyController’, function ($scope, $element) { // injected arguments });

When the methods like directive linker function don’t receive arguments through dependency injection, you just pass the scope object without using dollar prefix i.e. scope. The reason is the passing arguments are received by its caller.

module.directive(‘myDirective’, function () // injected arguments here {

return {

  • linker function does not use dependency injection link: function (scope, el, attrs) {
  • the calling function will passes the three arguments to the linker: scope, element and attributes, in the same order

}

};

});

In the case of non-dependency injected arguments, you can give the name of injected objects as you wish. The above code can be re-written as:

module.directive(“myDirective”, function () {

return {

link: function (s, e, a) {

  • s == scope
  • e == element
  • a == attributes

}

};

});

In short, in case of DI the scope object is received as $scope while in case of non-DI scope object is received as scope or with any name.

Q38. How AngularJS is compiled?

Ans. Angular’s HTML compiler allows you to teach the browser new HTML syntax. The compiler allows you to attach new behaviors or attributes to any HTML element. Angular calls these behaviors as directives.

AngularJS compilation process takes place in the web browser; no server side or pre-compilation step is involved. Angular uses $compiler service to compile your angular HTML page. The angular’ compilation process begins after your HTML page (static DOM) is fully loaded. It happens in two phases:

  1. Compile – It traverse the DOM and collect all of the directives. The result is a linking function.
  2. Link – It combines the directives with a scope and produces a live view. Any changes in the scope model are reflected in the view, and any user interactions with the view are reflected in the scope model.

The concept of compile and link comes from C language, where you first compile the code and then link it to actually execute it. The process is very much similar in AngularJS as well.

Q39. How AngularJS compilation is different from other JavaScript frameworks?

Ans. If you have worked on templates in other java script framework/library like backbone and jQuery, they process the template as a string and result as a string. You have to dumped this result string into the DOM where you wanted it with innerHTML()

AngularJS process the template in another way. It directly works on HTML DOM rather than strings and manipulates it as required. It uses two way data-binding between model and view to sync your data.

Q40. What directives are used to show and hide HTML elements in AngularJS?

Ans. ng-show and ng-hide directives are used to show and hide HTML elements in the AngularJS based on an expression. When the expression is true for ng-show or ng-hide, HTML element(s) are shown or hidden from the page. When the expression is false for ng-show or ng-hide, HTML element(s) are hidden or shown on the page.

ng-show Visible

ng-hide Invisible

Q41. Explain directives ng-if, ng-switch and ng-repeat?

Ans. ng-if – This directive can add / remove HTML elements from the DOM based on an expression. If the expression is true, it add HTML elements to DOM, otherwise HTML elements are removed from the DOM.

ng-if Visible

ng-switch – This directive can add / remove HTML elements from the DOM conditionally based on scope expression.

Shown when case is 1

Shown when case is 2

Shown when case is anything else than 1 and 2

ng-repeat – This directive is used to iterate over a collection of items and generate HTML from it.

  • {{ name}}

Q42. What are ng-repeat special variables?

Ans. The ng-repeat directive has a set of special variables which you are useful while iterating the collection.

These variables are as follows:

  • $index
  • $first
  • $middle
  • $last
  • [{{$index + 1}}{{name}}is a {{friend.gender}}.

(first element found)

(middle element found)

(last element found)

Output

The $index contains the index of the element being iterated. The $first, $middle and $last returns a boolean value depending on whether the current item is the first, middle or last element in the collection being iterated.

Q43. What is ng-include and when to use it?

Ans. ng-include is a directive which is used to include external HTML fragments from other files into the view’s HTML template.

For exampleindex.html file can be added inside the div element by using ng-include directive as an attribute.

ng-include directive is limited to load HTML fragments file from same domain but it doesn’t work for cross-domain i.e. it can’t load the HTML fragments file from different domains.

 Q44. What angular components can be defined within AngularJS templates?

Ans. AngularJS templates can have following angular elements and attributes:

  1. Directive
  2. Angular Markup (‘{{}}’)
  3. Filters
  4. Form Controls

Q45. What is data binding in AngularJS?

Ans. AngularJS data-binding is the most useful feature which saves you from writing boilerplate code (i.e. the sections of code which is included in many places with little or no alteration). Now, developers are not responsible for manually manipulating the DOM elements and attributes to reflect model changes. AngularJS provides two-way data-binding to handle the synchronization of data between model and view.

Q46. What is issue with two-way data binding?

OR

Why one-way data binding is introduced?

Ans. In order to make data-binding possible, Angular uses $watch APIs to observe model changes on the scope. Angular registered watchers for each variable on scope to observe the change in its value. If the value, of variable on scope is changed then the view gets updated automatically.

This automatic change happens because of $digest cycle is triggered. Hence, Angular processes all registered watchers on the current scope and its children and checks for model changes and calls dedicated watch listeners until the model is stabilized and no more listeners are fired. Once the $digest loop finishes the execution, the browser re-renders the DOM and reflects the changes.

By default, every variable on a scope is observed by the angular. In this way, unnecessary variable are also observed by the angular that is time consuming and as a result page is becoming slow.

Hence to avoid unnecessary observing of variables on scope object, angular introduced one-way data binding.

Q47. How AngularJS handle data binding?

Ans. AngularJS handle data-binding mechanism with the help of three powerful functions: $watch(), $digest() and $apply(). Most of the time AngularJS will call the $scope.$watch() and $scope.$digest() functions for you, but in some cases you may have to call these functions yourself to update new values.

Q48. Explain AngularJS scope life-cycle?

Ans. Scope data goes through a life cycle when the angular app is loaded into the browser. Understanding the scope life cycle will help you to understand the interaction between scope and other AngularJS components.

The scope data goes through the following life cycle phases:

  1. Creation – This phase initialized the scope. The root scope is created by the $injector when the application is bootstrapped. During template linking, some directives create new child scopes.

A digest loop is also created in this phase that interacts with the browser event loop. This digest loop is responsible to          update DOM elements with the changes made to the model as well as executing any registered watcher functions.

  1. Watcher registration – This phase registers watches for values on the scope that are represented in the These watches propagate model changes automatically to the DOM elements.

You can also register your own watch functions on a scope value by using the $watch() function.

  1. Model mutation – This phase occurs when data in the scope changes. When you make the changes in your angular app code, the scope function $apply() updates the model and calls the $digest() function to update the DOM elements and registered watches.

When you do the changes to scope inside your angular code like within controllers or services, angular internally call $apply() function for you. But when you do the changes to the scope outside the angular code, you have to call $apply() function explicitly on the scope to force the model and DOM to be updated correctly.

  1. Mutation observation – This phase occurs when the $digest() function is executed by the digest loop at the end of $apply() When $digest() function executes, it evaluates all watches for model changes. If a value has been changed, $digest() calls the $watch listener and updates the DOM elements.
  2. Scope destruction – This phase occurs when child scopes are no longer needed and these scopes are removed from the browser’s memory by using $destroy() function. It is the responsibility of the child scope creator to destroy them via scope.$destroy() API.

This stop propagation of $digest calls into the child scopes and allow the memory to be reclaimed by the browser garbage collector.

Q49. When to use $destroy() function of scope?

Ans. $destroy() – This function permanently detached the current scope with all of its children from the parent scope. This is required when child scopes are no longer needed. Hence, $destroy() function is called to remove these scopes from the browser’s memory.

When $destroy() is called all the watchers and listeners get removed and the object which represented the scope becomes eligible for garbage collection.

Q50. What is difference between $evalAsync and $timeout?

Ans. $evalAsync – This executes the expression on the current scope on later time. The $evalAsync makes no guarantees as to when the expression will be executed, only that:

  1. If code is queued using $evalAsync from a directive, it will run after the DOM has been manipulated by Angular, but before the browser renders.
  2. If code is queued using $evalAsync from a controller, it will run before the DOM has been manipulated by Angular and before the browser renders.

$timeout – This also executes the expression on the current scope on later time. When the code is queued using $timeout, it will run after the DOM has been manipulated by Angular and after the browser renders which may cause flicker in some cases.

Q51. What is the difference between $watch and $observe?

Ans. $watch is a method on the scope object which is used to watch expressions. The expression can be either strings or functions. It can be called wherever you have access to scope (a controller or a directive linking function).

$observe is a method on the attrs object which is only used to observe the value change of a DOM attribute. It is only used inside directives.

Note – All $observes and $watches are checked on every digest cycle.

 Q52.   What is the difference between $parse and $eval?

Ans. $parse and $eval both operate on angular expressions i.e. {{ expression }}.

$eval is a scope method which executes an expression on the current scope and returns the result.

scope.a = 1;

scope.b = 2;

scope.$eval(‘a+b’);       // 3

$parse is an Angular service which converts an expression into a function. Then function can be invoked and passed a context (usually scope) in order to retrieve the expression’s value.

dotnet-tricks.com

Also, if the expression is assignable then the returned function will have an assign property. The assign property is a function that can be used to change the expression’s value on the given context.

Q53. What is Isolate Scope and why it is required?

Ans. By default, directives have access to the parent scope in AngularJS apps. Hence, you can write your custom directive code based on parent scope. If the parent scope changes at all the directive is no longer useful.

angular.module(‘mydirective’).directive(‘sharedScope’, function () { return {

template: ‘Name: {{emp.name}} Address: {{emp.address}}’

};

});

The shared scope allows the parent scope to flow down into the directive but the Isolate scope doesn’t allow the parent scope to flow down into the directive.

Creating Isolate Scope

You can isolate the scope in a directive by adding a scope property into the directive as given below:

angular.module(‘mydirective’).directive(‘sharedScope’, function () { return {

scope: {},

template: ‘Name: {{emp.name}} Address: {{emp.address}}’

};

});

Q54. Does AngularJS support MVC?

Ans. AngularJS is a MVC framework. It does not implement MVC in the traditional way, but rather something closer to MVVM Model-View-ViewModel).

Q55. What is Model in AngularJS?

Ans. Models are plain old JavaScript objects that represent data used by your app. Models are also used to represent your app’s current state.

Q56. What is ViewModel in AngularJS?

Ans. A viewmodel is an object that provides specific data and methods to maintain specific views. Basically, it is a $scope object which lives within your AngularJS app’s controller. A viewmodel is associated with a HTML element with the ng-model and ng-bind directives.

Q57. What is Controller in AngularJS?

Ans. The controller defines the actual behavior of your app. It contains business logic for the view and connects the model to view with the help of $scope. A controller is associated with a HTML element with the ng-controller directive.

Creating Controller

Using Controller

Id:

Name:

Author:

Q58. How to share information between controllers in AngularJS?

OR

What are the ways to communicate between controllers in AngularJS?

Ans. There are various different ways to share data between controllers in an AngularJS app. The most commonly used are Scope, Service, Factory and Providers.

Q59. What is $emit, $broadcast and $on in AngularJS?

Ans. AngularJS provides $on, $emit, and $broadcast services for event-based communication between controllers.

$emit – It dispatches an event name upwards through the scope hierarchy and notify to the registered $rootScope.Scope listeners. The event life cycle starts at the scope on which $emit was called. The event traverses upwards toward the root scope and calls all registered listeners along the way. The event will stop propagating if one of the listeners cancels it.

Broadcasting

Parent Controller

Emit Message : {{message}}

Child Controller

Output

$on – It listen on events of a given type. It can catch the event dispatched by $broadcast and $emit.

Note – If there is no parent-child relation between your scopes you can inject $rootScope into the controller and broadcast the event to all child scopes but you cannot emit your event. You can emit your event only when you have parent-child relation and event propagation is initiated by child. However, $emit can fire an event only for all $rootScope.$on listeners.

Q60. What is View in AngularJS?

Ans. The view is responsible for presenting your models data to end user. Typically it is the HTML markup which exists after AngularJS has parsed and compiled the HTML to include rendered markup and bindings.

Q61. How to apply validation in AngularJS?

Ans. AngularJS provides you built-in validation directives to validate form client side. This makes your life pretty easy to handle client-side form validations without adding a lot of extra effort. AngularJS form validations are based on the HTML5 form validators.

AngularJS directives for form validation

Here is a list of AngularJS directive which can be applied on an input field to validate its value.

Q62. How to do custom form validation in AngularJS?

Ans. AngularJS allows you to create your own custom validation directives. For example, you have to compare password and confirm password fields. To achieve this task, you have to make a custom directive that will be fired whenever the password or confirm password changes.

Creating custom directive to compare password and confirm password fields

//defining module

var myapp = angular.module(‘myapp’, []);

//creating custom directive

myapp.directive(‘ngCompare’, function () {

return {

require: ‘ngModel’,

link: function (scope, currentEl, attrs, ctrl) {

var comparefield = document.getElementsByName(attrs.ngCompare)[0]; //getting first element

compareEl = angular.element(comparefield);

//current field key up

currentEl.on(‘keyup’, function () {

if (compareEl.val() != “”) {

var isMatch = currentEl.val() === compareEl.val(); ctrl.$setValidity(‘compare’, isMatch); scope.$digest();

}

});

//Element to compare field key up

compareEl.on(‘keyup’, function () {

if (currentEl.val() != “”) {

var isMatch = currentEl.val() === compareEl.val(); ctrl.$setValidity(‘compare’, isMatch); scope.$digest();

}

});

}

}

});

Using above created custom directive

Your password is required.

Confirm password doesn’t match.

Q63. What are different Angular form properties?

Ans. Angular provides properties on form which help you to get information about a form or its inputs and to validate them.

$valid – It is a boolean property that tells whether the form or it’s inputs are valid or not. If all containing form and controls are valid, then it will be true, otherwise it will be false.

Syntax

formName.$valid

formName.inputFieldName.$valid

$invalid – It is a boolean property that tells whether the form or it’s inputs are invalid or not. If at least one containing form and control is invalid then it will be true, otherwise it will be false.

Syntax

formName.$invalid

formName.inputFieldName.$invalid

$pristine – It is a boolean property that tells whether the form or it’s inputs are unmodified by the user or not. If the form or its inputs are unmodified by the user, then it will be true, otherwise it will be false.

Syntax

formName.inputFieldName.$pristine

$dirty – It is a boolean property that is actually just reverse of pristine i.e. it tells whether the form or it’s inputs are modified by the user or not. If the form or its inputs are modified by the user, then it will be true, otherwise it will be false.

Syntax

formName.$dirty

formName.inputFieldName.$dirty

$error – This is an object hash which contains references to all invalid controls or forms. It has all errors as keys: where keys are validation tokens (such as required, url or email) and values are arrays of controls or forms that are invalid with given error. For a control, if a validation fails then it will be true, otherwise it will be false.

Syntax

formName.$error

formName.inputFieldName.$error

Q64. What are different states of a form in AngularJS?

Ans. The AngularJS form goes to the following states, starting from the form rendering and when the user has finished the filling of form.

State 1: pristine and invalid – When the form is first time rendered and the user has not interacted with the form yet.

State 2: dirty and invalid – User has interacted with the form, but form validity has not been satisfied, yet.

State 3: dirty and valid – User has finished the filling of form and the entire form validations has been satisfied

Q65. What is Service in AngularJS?

Ans. A service is a reusable singleton object which is used to organize and share code across your app. A service can be injected into controllers, filters, directives.

AngularJS offers several built-in services (like $http, $provide, $resource, $window, $parse) which always start with $ sign.

Q66. What is difference between value and constant?

Ans. Value and Constant are simple objects which are used to share data globally with in a module.

Value – A value can be a number, string, date-time, array or object. You can also register a function as a value.

Values are typically used as configuration which is injected into factories, services or controllers.

//define module

var app = angular.module(‘app’, []);

//define value

app.value(“numberValue”, 100);

app.value(“stringValue”, “dotnet-tricks.com”);

app.value(“objectValue”, { name: “dotnet-tricks.com”, totalUsers: 120000 });

Constant – A constant is like as value. The difference between a value and a constant service is that constant service can be injected into a module configuration function i.e. config() but value service cannot be.

//define module

var app = angular.module(‘app’, []);

//define constant

app.constant(“mynumberValue”, 200);

app.constant(“mystringValue”, “webgeekschool.com”);

//module configuration function

app.config(function (mynumberValue) { //here value objects can’t be injected console.log(“Before:” + mynumberValue);

mynumberValue = “New Angular Constant Service”;

console.log(“After:” + mynumberValue);

});

Q67. What is $q service and when to use it?

Ans. $q is a service that helps you to run functions asynchronously, and use their return values when they have done processing.

$q service is said to be inspired by Chris Kowal’s Q library which allow users to monitor asynchronous progress by providing a “promise” as a return from a call.

It is good when you need to process a number of asynchronous activities simultaneously. The $q.all() function lets you trigger several callbacks at the same time, and use a single then function to join them all together.

var first = $http.get(“/app/data/first.json”),

second = $http.get(“/app/data/second.json”),

third = $http.get(“/app/data/third.json”);

$q.all([first, second, third]).then(function (result) { var tmp = [];

angular.forEach(result, function (response) {

tmp.push(response.data);

});

return tmp;

}).then(function (tmpResult) {

$scope.combinedResult = tmpResult.join(“, “);

});

Q68. What is the difference between Kris Kowal’s Q and $q?

Ans. There are two main differences between Kris Kowal’s Q and $q:

  1. $q is integrated with the $rootScope.Scope Scope model observation mechanism in angular, which means faster propagation of resolution or rejection into your models and avoiding unnecessary browser repaints, which would result in flickering UI.
  2. Q has many more features than $q, but that comes at a cost of bytes. $q is tiny, but contains all the important functionality needed for common async tasks.

Q69. What is Restangular?

Ans. Restangular is an Angular service specifically designed simply to fetch data from the rest of the world. To use Restangular you need to link the restangular.js file and include restangular resource as a dependency within your angular app.

var app = angular.module(‘myApp’, [‘restangular’]);

app.controller(‘MainController’,function ($scope, Restangular) { //TO DO:

});

Q70. What are the advantages of Restangular over $resource and $http?

Ans. Restangular has several features that distinguish it from $resource:

  1. It uses promises.
  2. You can use this in $routeProvider.resolve.
  3. It doesn’t have all those $resource bugs like trailing slashes, additional: in the URL, escaping information, expecting only arrays for getting lists, etc.
  4. It supports all HTTP methods.
  5. It supports ETag out of the box.
  6. It supports self-linking elements if you receive from the server some item that has a link to itself, you can use that to query the server instead of writing the URL manually.
  7. You don’t have to create one $resource object per request.
  8. You don’t have to write or remember ANY URL like $resource. You just write the name of the resource you want to fetch and that’s it.
  9. It supports nested RESTful resources.
  10. Restangular lets you create your own methods.
  11. Support for wrapped responses.

Q71. What is difference between $window and window in AngularJS?

Ans. $window is an Angular service which reference to the browser’s window object. The window object is globally available in JavaScript; it causes testability problems, because it is a global variable. Angular refer to it through the $window service, so that it can be overridden, removed or mocked for testing.

Q72. What is difference between $document and window.document in AngularJS?

 Ans. $document is an Angular service which reference to the browser’s window.document object.

$document title:

window.document title:

Q73. What is difference between $interval and window. setInterval in AngularJS?

Ans. $interval is an Angular service which wraps the browser’s window. setInterval() function. It is also used to call a JavaScript function repeatedly within a time interval.

var app = angular.module(“app”, []);

app.controller(“MyController”, function ($scope, $interval) { $interval(callAtInterval, 3000);

});

function callAtInterval() {

console.log(“Interval occurred”);

}

Q74. What is Routing in AngularJS?

Ans. AngularJS Routing helps you to divide your app into multiple views and bind different views to Controllers. The magic of Routing is taken care by an AngularJS service $routeProvider. $routeProvider service provides method when() and otherwise() to define the routes for your app. Routing has dependency on ngRoute module.

Defining Route for your application

Q75. What is AngularUI router and how it is different from ngRoute?

Ans. The UI-Router is a routing framework for AngularJS built by the AngularUI team. Unlike ngRoute, it changes your angular app views based on state of the app and not based on the route URL (ngRoute).

The ui-router helps you to create nested views, use multiple views on the same page, have multiple views that control a single view, and more.

To use it you need to include reference of ui-router.js file into your angular app.

Q76. What is $injector and $inject?

Ans. $injector is a service which is used to invoke controller functions, service functions, filter functions, and any other function that might need dependencies as parameters. Angular creates only a single $injector object when an application is bootstrapped and uses that object for invoking.

{{value()}}

$inject is property which is used to inject the dependencies of a function as an array of strings.

Q77. What is Dependency Injection in AngularJS?

Ans. Dependency Injection (DI) is a software design pattern that deals with how components get hold of their dependencies. AngularJS comes with a built-in dependency injection mechanism. You can divide your AngularJS app into multiple different types of components which AngularJS can inject into each other.

There are following three ways of injecting dependencies into your code:

  1. Implicitly from the function parameter names

  1. Using the $inject property annotation

  1. Using the inline array annotation

Q78. How to do Language Internationalization in AngularJS?

Ans. The angular-translate is an AngularJS module that brings i18n (internationalization) and l10n (localization) into your Angular app. It allows you to create a JSON file that represents translation data as per language. These languages specific JSON files can be lazy-loads from the server only when necessary. The angular-translate library (angular-translate.js) also provides built-in directives and filters that make the process of internationalizing simple.

AngularJS Internalization

{{ ‘TITLE’ | translate }}

{{ ‘PARA’ | translate }}

Q79. What is i18n and L10n?

Ans. i18n means Internationalization, where 18 stands for the number of letters in word Internationalization between the first i and last n. It is the process of developing products in such a way that they can be localized for languages and cultures easily.

L10n means Localization, where 10 stand for the number of letters in word Localization between the first L and last n. It is the process of adapting applications and text to enable their usability in a particular culture.

Q80. What is $locale service?

Ans. $locale service provides localization rules for various Angular components. As of now the only public api is: id – {string}

For example, a locale id is formatted as: languageId-countryId (e.g. en-us)

Q81. What is a locale ID?

Ans. A locale is a specific geographical, political, or cultural region. The most commonly used locale ID consists of two parts: language code and country code. For example, en-US, en-AU, hi-IN are all valid locale IDs that have both language codes and country codes.

Q82. How to manage cookie in AngularJS?

Ans. AngularJS provides ngCookies module for reading and writing browser cookies. To use it include the angular-cookies.js file and set ngCookies as a dependency in your angular app. This module provides two services for cookie management: $cookies and $cookieStore.

Q83. What is difference between $cookies and $cookieStore service?

Ans. $cookies – This service provides read/write access to browser’s cookies.

If you want to use existing cookie solution, say read/write cookies from your existing server session system then use $cookie.

var app=angular.module(‘cookiesExample’, [‘ngCookies’]);

app.controller(‘ExampleController’, function ($cookies) { // Retrieving a cookie

var favoriteCookie = $cookies.myFavorite;

// Setting a cookie

$cookies.myFavorite = ‘meal’;

});

$cookiesStore – $cookieStore is a thin wrapper around $cookies. It provides a key-value (string-object) storage that is backed by session cookies. The objects which are put or retrieved from this storage are automatically serialized or deserialized by angular to JSON and vice versa.

If you are creating a new solution which will persist cookies based on key/value pairs, use $cookieStore.

var app=angular.module(‘cookieStoreExample’, [‘ngCookies’]);

app.controller(‘ExampleController’,function ($cookieStore) { // Put cookie

$cookieStore.put(‘myFavorite’, ‘meal’);

// Get cookie

var favoriteCookie = $cookieStore.get(‘myFavorite’);

// Removing a cookie

$cookieStore.remove(‘myFavorite’);

});

Q84. How to handle mobile browsers/devices events in AngularJS?

Ans. Mobile browsers/devices deal with events differently than desktop browsers. The AngularJS provide ngTouch library (angular-touch.js) to detect mobile browsers/devices events.

For example, Mobile browsers detect a tap event and then wait for second event about 300 ms if any. So if we’re double-tapping the device then after this delay the browser fires a click event.

In this way this delay can make our apps unresponsive. Hence, instead of dealing with the click event, we can detect touch event using ngTouch library. It handles touch detection for us through the ng-click directive. Hence it will take care of calling the correct click event for mobile.

Q85. How to detect swipe event in mobile browsers/devices in AngularJS?

Ans. The ngTouch library provides swipe directives to capture user swipes, either left or right across the screen. These events are useful when the user want to swipe to the next photo gallery photo or to a new portion of our app.

The ngSwipeLeft directive detects when an HTML element is swiped from the right to the left and the ngSwipeRight directive detects when an HTML element is swiped from the left to the right.

Q86. How to do animation with the help of AngularJS?

Ans. AngularJS 1.2 comes with animation support via ngAnimate module. To enable animations within your angular app, you need to link the angular-animate.js file and include ngAnimate module as a dependency within your angular app.

Q87. What directives support animations?

Ans. The following directives support animations:

  1. ngRepeat – It supports enter, leave and move animations.
  2. ngInclude – It supports enter and leave animations.
  3. ngView – It supports enter and leave animations.
  4. ngIf – It supports enter and leave animations.
  5. ngSwitch – It supports enter and leave animations.
  6. ngClass – It supports addClass and removeClass animations.
  7. ngShow & ngHide – These support addClass and removeClass animations.

Q88. How to securely parse and manipulate your HTML data in AngularJS?

Ans. AngularJS provides ngSanitize module to securely parse and manipulate HTML data in your application.

To use it include the angular-sanitize.js file and set ngSanitize as a dependency in your angular app.

var app = angular.module(‘sanitizeExample’, [‘ngSanitize’]); app.controller(‘ExampleController’,function ($scope, $sce) {

var snippet =’

an html\n’ +

click here\n snippet

‘;

$scope.trustedSnippet = $sce.trustAsHtml(snippet); //sce=Strict Contextual Escaping

});

The snippet may contain HTML, CSS, URLs and JavaScript code which you want to safely render in your app.

Q89. What is Angular 2.0?

Ans. Angular 2.0 is being written with AtScript, but that doesn’t mean you have to write your application code with AtScript or know anything about AtScript to use Angular 2.0. You can easily write with TypeScript, ES6, ES5, CoffeeScript etc. whatever you like. It is still in development phase (at the time of writing this book).

Q90. What is AtScript?

Ans. AtScript is Google’s new superset for JavaScript. It enhances JavaScript with new features to make it more robust. It is not only designed to run on top of ECMAScript 5 and ECMAScript 6, but on the top of Microsoft’s superset TypeScript language as well.

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