What are different ways to invoke a directive?

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

Method	Syntax
As an attribute	<span my-directive></span>
As a class	<span class="my-directive: expression;"></span>
As an element	<my-directive></my-directive>
As a comment	<!-- directive: my-directive expression -->

How to create custom directives in AngularJS?

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: "<div>{{ myName }}</div>",// 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:

}

}

});

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

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.

What are Directives in AngularJS?

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.

How AngularJS expressions are different from the JavaScript expressions?

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.

What are Expressions in AngularJS?

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 }}

What are Filters in AngularJS?

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


<script type="text/javascript">

{ { 14 | currency } } //returns $14.00 </script>

What is Angular Prefixes $ and $$?

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.

What is Global API?

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.

When dependent modules of a module are loaded?

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.

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

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.