AngularJS Interview Questions

AngularJS is a JavaScript framework that is used for making rich and extensible web applications.

It runs on plain JavaScript and HTML, hence you don’t need any other dependencies to make it work. AngularJS is perfect for Single Page Applications (SPA). It is basically used for binding JavaScript objects with HTML UI elements.

Its features include:

• The Template (View)
• The Scope (Model)
• The Controller (Controller)
• Services
• Filters

Data binding is an automatic attunement of data between the view and model components.

There are several differences between AngularJs and JavaScript expressions:

• We can write AngularJs expressions in HTML, but we cannot write JavaScript expressions in HTML.
• We cannot use conditional iterations, loops, and exceptions in AngularJs, but we can use all of these conditional properties in JavaScript expressions.
• Filters are supported in AngularJs whereas filters are not supported in JavaScript.

To set up an Angular App we must follow certain steps as mentioned below:

• angular.module will be created at first.
• A controller will be assigned to the module.
• The module will be linked with the HTML template(i.e. UI or View) with an angular app(ng-app).
• The HTML template will be linked with the controller(i.e JS) with an ng-controller directive.

The angular modules collectively define an angular application where we can write the angular code.

Modules contain the different parts of an angular application. A module is created by angular.module function in angular.

Three directive scopes are available in AngularJs.

• Parent scope – Whatever change you make in your directive that comes from the parent scope, will also reflect in the parent scope, and it is also a default scope.
• Child scope – It is a nested scope that inherits a property from the parent scope. Also if any properties and functions on the scope are not connected with the parent scope directive, then a new child scope directive is created.
• Isolated scope – It is reusable and is used when we build a self-contained directive. It is only used for private and internal use which means it does not contain any properties of the parent scope.

First, we have to create a service. Service is used to share the data between controllers in AngularJs in a very lucid, easy, and fastest way. We use events, $parent, next sibling, and controller by using $rootScope.

It is a part of the process of data binding in AngularJs. It compares the old and new version of the scope model value in each digest cycle.

The digest cycle is triggered automatically. We can also enhance the usability by using $apply () if we want to trigger the digest cycle manually.

One-way binding is used to bind the data from the model to view without updating the HTML template or view automatically.

Thus in order to update the HTML template, we need to write a custom code which will update the view every time whenever a data is binded from model to view.

Whereas, two-way binding is used to bind the data from the model to view and vice versa(i.e view to model) by automatically updating the HTML template without writing any custom code.

Given below are the differences.

• SessionStorage – The data is stored for a particular session. The data will be lost whenever the browser tab will be closed or after some particular session. The maximum size stored can be up to 5MB.
• LocalStorage – The data is stored with no expiration date. The data can only be cleared by JavaScript or by clearing the browser cache. The storage limit is maximum than the sessionStorage and cookie.
• Cookies – It stores the data that has to be sent back to the server with some requests. The cookies expiration varies on the type and duration set from either the server-side or client side. Maximum size stored can be less than 4KB.

It is the $routeProvider that helps in navigating between different pages/links without separately loading the page/link whenever a user clicks on a link.

ngRoute config() method is used to configure the routeProvider.

In AngularJs $scope is used to achieve dependency injection and scope is used for linking between View (i.e HTML) and Controller (i.e JS).

$$ variable in AngularJS is used as a private variable, as it is used to prevent accidental code collision with the user code.

Whereas $ prefix can be used to denote angular core functionalities (like a variable, parameter, property, or method).

Manipulation of DOM is in directives and apart from this, it should not exist in controllers’ services or anywhere else.

To show one-time binding we have to use “::” in front of the scope.

It is a web application which loads a single HTML page and dynamically updates the page as the user connects with the app.

By using AJAX and HTML a fluid and responsive web app can be created by SPA without invariant page reloads. Through this, we can make responsive UI with no page flicker.

AngularJs supports both one-way and two-way binding.

In one way binding if we change the data model, then there will be no dynamic change that you will see in view but in two way binding, there will be a dynamic change whenever a change will be made in the data model.

The binding directives include:

• ng-bind
• ng-bind-html
• ng-bind-template
• ng-non-bindable
• ng-model

ng-bind: It is a directive that replaces the content of the HTML element with the value of the assigned variable or expression.

The content of the HTML element will change by changing the value of the variable or expression.

It is like ({{expression}}) and the syntax for this is,

<ANY ELEMENT ng-bind="expression"> </ANY ELEMENT>

ng-bind-html: It is a directive that binds the content to the HTML element(view) in a secure way. $sanitize service is used to sanitize the content to bind into an HTML element. To do this ‘angular-sanitize.js’ must be included in our application.

Syntax to write this,

<ANY ELEMENT ng-bind-html=" expression "> </ANY ELEMENT>

ng-bind-template: It replaces the text content of the element by interpolation of the template. It can contain multiple double curly markups.

<ANY ELEMENT ng-bind-template= " {{expression1}} {{expression2}} … {{expression n}} "> </ANY ELEMENT>

Ng-non-bindable: It specifies AngularJs to not compile the content of this HTML element and its child nodes.

<ANY ELEMENT ng-non-bindable > </ANY ELEMENT>

This can be a leap hop with the custom HTML input form control( like input, textarea, and select) to the application data. It provides form validation behavior with two-way binding.

<input ng-bind="expression"/>

It is quite similar to service, factories implement a module pattern in which we use a factory method to generate an object which is used for building models.

In a factory, a method object is returned at the end by creating a new object and adding functions as properties. Syntax:

module.factory(‘factoryName, function);

It renders or iterates over a collection of items and creates DOM elements. It regularly monitors the source of data to re-render a template in response to a change.

Syntax:

<table class="table table-bordered">

      <tr ng-repeat="student stuDetails">

            <td>{{stu.name}} </td>

           <td> {{stu. grade}} </td>

     </tr>

</table>

A controller is a JavaScript function that is bound to the specified scope. Angular instantiates the new controller object and injects the new scope as a dependency.

A controller can be used to set up the initial state of the scope object and to add behavior to the object.

A controller cannot be used to share code or state across controllers, but instead of the Angular service can be used.

<Any ng-Controller=” expression”>

</Any>

<div ng-app="mainApp" ng-controller="SimpleController">

</div>

The main work of filters is to modify the data so that it can be merged into an expression or directive by using a pipe character (it is used for applying filters in an angular symbol of a pipe which is (|) or this is the symbol).

A filter formats the value of an expression for a display to the user. They can be used in view templates, controllers, or services, and we can easily create our own filter as well. A filter is a module provided by AngularJS.

There are nine components of a filter that are provided by AngularJS.

Examples: currency, date, filter, JSON, limit, etc.

It is used to define the AngularJs Application. It appoints the root element of an AngularJs application and it is kept near the or tag.

We can define any number of ng-app directives inside the HTML document, but only one AngularJS application can be bootstrapped automatically (auto-bootstrapped) and the other applications need to be bootstrapped manually.

Example:

<div ng-app="">

<p>My first expression: {{157 + 122}} </p>

</div>

It is used to conditionally exchange the structure of DOM on a template that is based on a scope-based expression.

This directive lets you show or hide the HTML element depending on the expression.

<element ng-switch="expression">

<element ng-switch-when="value"></element>

It allows you to specify the custom behavior on a double click event of the mouse on a web page. We can use it (ng-dblclick) as an attribute of the HTML element like,

<ANY_HTML_ELEMENT ng-dblclick="{expression}">

...

</ANY_HTML_ELEMENT>

ng-include helps to include different files on the main page. The ng-include directive includes HTML from an external file.

The included content will be included as child nodes of the specified element. The value of the ng-include attribute can also be an expression, returning a filename.

By default, the included file must be located on the same domain as the document.

<div ng-include="myFile.htm"></div>

ng-click can be used in scenarios like when you click on a button or when you want to do any operation. It tells AngularJS what to do when an HTML element is clicked.

Example:

<button ng-click="count = count + 1" ng-init="count=0">OK</button>

The above code will increase the count variable by one whenever the button is clicked.