AngularJS expressions are JavaScript-like code snippets that are used to bind data to HTML elements or attributes within an AngularJS application. These expressions are usually enclosed in double curly braces ({{ }}) and are placed in the HTML code to display dynamic content. AngularJS expressions are evaluated in the context of the current scope.
Here are some key points about AngularJS expressions:
-
Syntax: AngularJS expressions use a simple syntax with double curly braces, like this:
{{ expression }}. -
Data Binding: Expressions are commonly used for data binding, allowing you to display dynamic content by binding variables from the AngularJS scope to HTML elements.
Example:
<p>{{ message }}</p>In this example, if there's a variable named
messagein the current scope, its value will be displayed inside the paragraph element. -
JavaScript-Like: AngularJS expressions support a subset of JavaScript, allowing you to perform basic operations and evaluations.
Example:
<p>{{ 2 + 2 }}</p>The result of the expression
2 + 2will be displayed in the paragraph. -
Filtering: AngularJS expressions can also use filters to format data before displaying it. Filters are added to expressions using a pipe (
|) symbol.Example:
<p>{{ message | uppercase }}</p>In this case, the
uppercasefilter is applied to themessagevariable, converting its value to uppercase before display. -
Avoid Side Effects: While expressions can contain code, it's generally recommended to keep them simple and avoid using them for complex logic or side-effect-causing operations. They are primarily meant for displaying data.
-
Context: Expressions are evaluated in the context of the current scope. If a variable is not found in the current scope, AngularJS will look for it in parent scopes until it reaches the root scope.
Example of using expressions in an AngularJS template:
<!DOCTYPE html>
<html lang="en" ng-app="myApp">
<head>
<meta charset="UTF-8">
<title>AngularJS Expressions</title>
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.8.2/angular.min.js"></script>
</head>
<body ng-controller="myController">
<h1>{{ greeting }}</h1>
<p>{{ "Current Date: " + currentDate | date:'fullDate' }}</p>
<script>
angular.module('myApp', []).controller('myController', function($scope) {
$scope.greeting = 'Hello, Angular!';
$scope.currentDate = new Date();
});
</script>
</body>
</html>
In this example, the {{ greeting }} expression binds the value of the greeting variable to the heading, and the {{ "Current Date: " + currentDate | date:'fullDate' }} expression concatenates a string with the formatted date and displays it in a paragraph.
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