AngularJS expressions are snippets of code that can be evaluated and interpolated into HTML templates. These expressions are written using double curly braces {{}} and can be used to display dynamic content on web pages.
Here’s an example of an AngularJS expression:
<div>
{{ message }}
</div>
In the above example, the expression is {{ message }}. This expression is evaluated by AngularJS, and the value of the message variable is inserted into the HTML template. If the message variable is set to “Hello, world!”, the resulting HTML output would be:
<div>
Hello, world!
</div>
AngularJS expressions can also include arithmetic operations, function calls, and other JavaScript code. For example:
<div>
{{ num1 + num2 }}
</div>
In the above example, the expression {{ num1 + num2 }} will evaluate the sum of num1 and num2, and display the result in the HTML template.
It’s important to note that AngularJS expressions are evaluated on the client side, not the server side. This means that they can be used to create dynamic, responsive web applications without requiring a page refresh.
Modules for AngularJS
A module in AngularJS is a container for related components such as controllers, directives, services, and filters. Use Angular to specify modules. A module method that takes a module name and an array of dependencies as parameters.
Here’s an example of a simple AngularJS module:
angular.module('myApp', []);
In the above example, we define a new module named myApp with no dependencies. This module can now be used to define and organize related components in our application.
To add components to a module, we can use the module’s controller, directive, service, or filter methods. For example, here’s how we can define a simple controller and add it to our myApp module:
angular.module('myApp', [])
.controller('myCtrl', function($scope) {
$scope.message = "Hello, world!";
});
In the above example, we define a new controller named myCtrl, which sets a message on the $scope object. This controller is added to the myApp module using the module’s controller method.
Once we have defined a module and added components to it, we can use the module in our HTML templates by adding it as a dependency to our main application module, like this:
angular.module('myApp', ['myModule']);
In the above example, we add the myModule module as a dependency to our main myApp module, so that we can use the components defined in myModule in our application.
Overall, modules provide a way to organize and modularize our AngularJS code, making it easier to manage and maintain as our application grows.
Directives for AngularJS
AngularJS directives are powerful tools that allow you to extend the HTML vocabulary of your web application, by creating custom HTML tags and attributes. They enable you to create reusable components and behaviors that can be applied to any element in your application.
Here’s a basic example of how you might define a directive in AngularJS:
angular.module('myApp')
.directive('myDirective', function() {
return {
restrict: 'E',
template: '<div>This is my custom directive!</div>',
link: function(scope, element, attrs) {
console.log('myDirective has been linked!');
}
};
});
This code defines a new directive called myDirective, which is restricted to be used as an element (restrict: ‘E’). It provides a simple template that will be used to replace the element’s content when it’s rendered on the page. The link function provides an opportunity to perform additional actions when the directive is linked to the element.
Here’s an example of how you might use the myDirective directive in your HTML:
<my-directive></my-directive>
Here’s another example of a directive that uses a more complex template and provides some additional functionality:
angular.module('myApp')
.directive('myOtherDirective', function() {
return {
restrict: 'A',
scope: {
message: '@myOtherDirective'
},
template: '<div>{{message}}</div>',
link: function(scope, element, attrs) {
console.log('myOtherDirective has been linked!');
element.on('click', function() {
alert('You clicked the myOtherDirective directive!');
});
}
};
});
This code defines a new directive called myOtherDirective, which is restricted to be used as an attribute (restrict: ‘A’). It defines a new isolated scope for the directive, with a single attribute called message. The template for this directive is more complex, and includes an AngularJS expression that will display the message attribute value.
The link function for this directive attaches a click event handler to the element, so that when it’s clicked, an alert dialog will be displayed.
Here’s an example of how you might use the myOtherDirective directive in your HTML:
<div my-other-directive="Hello, world!"></div>
When this code is rendered on the page, the resulting HTML will look like this:
<div>Hello, world!</div>
And if you click on the div, you’ll see an alert dialog that says “You clicked the myOtherDirective directive!”.
ng-model Directive in AngularJS
The ng-model directive in AngularJS is used to bind the value of an HTML input element to a property in the scope. It enables two-way data binding, which means that any changes made to the input field will automatically update the property in the scope, and vice versa.
Here’s an example of how to use ng-model in AngularJS:
HTML:
<div ng-controller="myController">
<input type="text" ng-model="message">
<p>{{ message }}</p>
</div>
JavaScript:
var app = angular.module('myApp', []);
app.controller('myController', function($scope) {
$scope.message = 'Hello World';
});
In this example, we have an input field with the ng-model directive, which binds the value of the input field to the “message” property in the scope. The “message” property is initially set to “Hello World” in the controller.
As the user types in the input field, the value of the “message” property in the scope is automatically updated. The updated value is then displayed in the paragraph element using AngularJS expression {{ message }}. This creates a two-way data binding between the input field and the scope property.
ng-model may be used with a variety of input components, including textboxes, checkboxes, radio buttons, and select boxes. You may also use ng-model with custom input directives that you design. The ng-model directive simplifies the development of data-driven apps in AngularJS.
Data Binding in AngularJS
Data binding in AngularJS is a significant feature that allows you to synchronize data between the display and the model. There are two forms of data binding: one-way binding and two-way binding.
One-way binding is when data flows in only one direction, from the model to the view or from the view to the model. Here’s an example of one-way binding in AngularJS:
HTML:
<div ng-controller="myController">
<p>{{ message }}</p>
</div>
JavaScript:
var app = angular.module('myApp', []);
app.controller('myController', function($scope) {
$scope.message = 'Hello World';
});
In this example, we have a paragraph element with an AngularJS expression {{ message }}. The “message” property is set in the controller and is displayed in the view using the AngularJS expression.
Two-way binding is when data flows in both directions, from the model to the view and from the view to the model. Here’s an example of two-way binding in AngularJS:
HTML:
<div ng-controller="myController">
<input type="text" ng-model="message">
<p>{{ message }}</p>
</div>
JavaScript:
var app = angular.module('myApp', []);
app.controller('myController', function($scope) {
$scope.message = 'Hello World';
});
In this example, we have an input element with the ng-model directive, which binds the value of the input field to the “message” property in the scope. As the user types in the input field, the value of the “message” property in the scope is automatically updated. The updated value is then displayed in the paragraph element using the AngularJS expression.
Data binding in AngularJS can be used with a wide range of elements and attributes, making it easy to create dynamic and interactive applications.