AngularJS is a popular JavaScript framework for creating web applications. It provides a lot of built-in directives to easily manipulate the DOM and data bindings. One of these directives is ngIf. In this article, we will discuss how to use the ngIf directive in AngularJS and how to create ng templates.
What is ngIf Directive?
In AngularJS, ngIf is a powerful directive that is used to conditionally display or remove an HTML element from the DOM. It evaluates the expression provided to it and if it returns true, it displays the content, otherwise, it removes it from the DOM.
Syntax:
The syntax for using ngIf is as follows:
<element ng-if="expression"> ... </element>
The ngIf directive expression should be a Boolean value based on which the element will be displayed or removed from the DOM.
How to use ngIf Directive in AngularJS?
Let's see how to use the ngIf directive in AngularJS using an example.
HTML Code:
<body ng-app="myApp" ng-controller="myCtrl">
<div ng-if="showMessage">
<h1>Welcome to AngularJS!</h1>
</div>
<button ng-click="toggleMessage()">Toggle Message</button>
</body>
JavaScript Code:
var app = angular.module("myApp", []);
app.controller("myCtrl", function($scope) {
$scope.showMessage = true;
$scope.toggleMessage = function() {
$scope.showMessage = !$scope.showMessage;
};
});
In the above code, we have created a simple AngularJS application with a controller called myCtrl. Inside the controller, we have defined a Boolean value called showMessage and set its initial value to true.
We have also defined a toggleMessage() function that toggles the value of showMessage between true and false.
In the HTML code, we have used the ngIf directive to display the message only if the showMessage value is true. We have also added a button that calls the toggleMessage() function to show or hide the message.
When you run this code, you will see a message "Welcome to AngularJS!" displayed on the screen. Clicking the button will remove or display the message based on the value of showMessage.
Creating ng templates with ngIf Directive:
Sometimes, you may need to conditionally display different content based on the value of an expression. In such cases, you can use ng templates with ngIf directive to conditionally render different content.
HTML Code:
<body ng-app="myApp" ng-controller="myCtrl">
<div ng-repeat="user in users">
<div ng-if="user.type === 'admin'" ng-include="'admin-template.html'"></div>
<div ng-if="user.type === 'user'" ng-include="'user-template.html'"></div>
</div>
</body>
JavaScript Code:
var app = angular.module("myApp", []);
app.controller("myCtrl", function($scope) {
$scope.users = [
{ type: "admin", name: "John" },
{ type: "user", name: "Peter" },
{ type: "admin", name: "Lisa" }
];
});
In the above code, we have created an AngularJS application with a controller called myCtrl. Inside the controller, we have defined an array of users with their types.
In the HTML code, we have used the ngIf directive to conditionally include different templates based on the type of the user.
If the user type is admin, it will include the admin-template.html file, and if the user type is user, it will include user-template.html.
Conclusion:
The ngIf directive in AngularJS is a powerful tool to conditionally display or remove elements from the DOM based on a Boolean expression. It can be used to create complex templates with different components conditionally rendered based on certain expressions.
We hope this article has provided you with enough information on the ngIf directive and templates. Keep experimenting with the different directives provided by AngularJS to create powerful web applications.
I can give you some further information about ngIf and ng templates in AngularJS.
Using ngIf Directive with ngSwitch
In addition to using the ngIf directive on its own, you can also use it in conjunction with the ngSwitch directive. The ngSwitch directive is used to conditionally render templates based on a specified value, similar to a switch statement in programming languages.
Here is an example of how you can use ngIf directive with the ngSwitch directive:
HTML Code:
<body ng-app="myApp" ng-controller="myCtrl">
<div ng-switch="value">
<div ng-switch-when="1" ng-include="'template1.html'"></div>
<div ng-switch-when="2" ng-include="'template2.html'"></div>
<div ng-switch-default ng-if="value > 2" ng-include="'template3.html'"></div>
</div>
<button ng-click="changeValue()">Change Value</button>
</body>
JavaScript Code:
var app = angular.module("myApp", []);
app.controller("myCtrl", function($scope) {
$scope.value = 1;
$scope.changeValue = function() {
if ($scope.value === 3) {
$scope.value = 1;
} else {
$scope.value++;
}
};
});
In this code, we have added an ngIf directive inside the ngSwitchDefault directive, which means this template will only be rendered if the value is greater than 2.
Using ngIf Directive with ngRepeat
Another way you can use ngIf directive is inside an ngRepeat directive. This allows you to conditionally render elements based on the data in your ngRepeat.
Here's an example of how you can use ngIf directive inside ngRepeat:
HTML Code:
<body ng-app="myApp" ng-controller="myCtrl">
<div ng-repeat="person in people">
<div ng-if="person.age >= 18">
<h3>{{person.name}}</h3>
<p>Age: {{person.age}}</p>
</div>
</div>
<button ng-click="addPerson()">Add Person</button>
</body>
JavaScript Code:
var app = angular.module("myApp", []);
app.controller("myCtrl", function($scope) {
$scope.people = [
{ name: "John", age: 20 },
{ name: "Lisa", age: 17 },
{ name: "Peter", age: 25 }
];
$scope.addPerson = function() {
$scope.people.push({ name: "Jane", age: 16 });
};
});
In this code, we have used the ngIf directive to only render the person if their age is 18 or higher.
Using ngTemplates
ngTemplates are reusable pieces of code that can be defined and then included in your app using the ngInclude directive. You can use ngIf directive inside your ngTemplates to conditionally render different content.
Here's an example of how you can use ngTemplates:
HTML Code:
<body ng-app="myApp">
<div ng-include="'my-template.html'"></div>
</body>
my-template.html Code:
<div>
<h3 ng-if="showTitle">{{title}}</h3>
<p>Lorem ipsum dolor sit amet, consectetur adipiscing elit.</p>
</div>
JavaScript Code:
var app = angular.module("myApp", []);
app.controller("myCtrl", function($scope) {
$scope.showTitle = true;
$scope.title = "Hello from ngTemplate!";
});
In this code, we have defined a simple ngTemplate called my-template.html and used the ngInclude directive to include it in our app. We also have used the ngIf directive inside the template to conditionally render the title.
Conclusion:
In AngularJS, the ngIf directive is used to conditionally render elements based on a specified Boolean expression. You can also use ngTemplates to create reusable pieces of code that can be included in your app using the ngInclude directive. By combining these two directives, you can create powerful templates that conditionally render different content based on certain expressions. Keep experimenting with different AngularJS directives to create powerful apps!
Popular questions
Sure, here are 5 questions and answers about Angular ngIf and ngTemplate directives:
Q1. What is the ngIf directive used for in AngularJS?
A1. The ngIf directive in AngularJS is used to conditionally display or remove an HTML element from the DOM based on a Boolean expression.
Q2. Can the ngIf directive be used inside other directives in AngularJS?
A2. Yes, you can use ngIf directive inside other directives such as ngSwitch and ngRepeat to conditionally render different content based on different expressions.
Q3. What are ngTemplates in AngularJS, and how do you use them?
A3. ngTemplates in AngularJS are reusable pieces of code that can be defined and included in your app using the ngInclude directive. You can use ngIf directive inside ngTemplates to conditionally render different content. To use ngTemplates, simply define them as HTML files and include them using ngInclude directive.
Q4. Can you give an example of how to use the ngIf directive inside an ngTemplate in AngularJS?
A4. Sure, here's an example:
<div>
<h3 ng-if="showTitle">{{title}}</h3>
<p>Lorem ipsum dolor sit amet, consectetur adipiscing elit.</p>
</div>
In this code, we have used ngIf directive to conditionally render the title inside an ngTemplate.
Q5. How do you toggle the value of a Boolean expression in AngularJS?
A5. To toggle the value of a Boolean expression in AngularJS, you can use the following code:
$scope.flag = true;
$scope.flag = !$scope.flag;
In this code, we have defined a Boolean expression called flag and toggled its value using the NOT operator (!).
Tag
"Ngif-Templates".
