AngularJS ngClass conditional

This tutorial will explore various ways to use ngClass with different conditional expressions.

In AngularJS, the ngClass directive is a powerful tool for dynamically applying CSS classes to HTML elements based on specified conditions. It allows you to manipulate the appearance of elements dynamically, making your web applications more interactive and responsive.

Basic Syntax

Here, the basic syntax of using ngClass is explained. It involves providing an object where the keys are class names, and the values are conditions. If the conditions evaluate to true, the associated class will be applied. The example provided shows a situation where the class ‘test’ is applied if obj.value1 equals ‘someothervalue’.

Example

<div ng-class="{'test': obj.value1 == 'someothervalue'}"></div>

Explanation:

• This code snippet demonstrates the basic syntax of ngClass.
• The ng-class directive takes an object as its value.
• The object has a key-value pair where the key is the CSS class name ('test'), and the value is a condition (obj.value1 == 'someothervalue').
• If the condition is true, the specified class will be applied to the element.

Using Logical Operators

This section expands on the basic syntax by introducing logical operators. The example demonstrates the use of the logical OR (||) operator to create a more complex condition. The ‘test’ class will be applied if either obj.value1 is equal to ‘someothervalue’ or obj.value2 is equal to ‘somethingelse’.

Example

<div ng-class="{'test': obj.value1 == 'someothervalue' || obj.value2 == 'somethingelse'}"></div>

Explanation:

• This code extends the basic syntax by introducing logical operators (|| in this case).
• The class 'test' will be applied if either obj.value1 is equal to 'someothervalue' or obj.value2 is equal to 'somethingelse'.

Applying ngClass inside ngRepeat

In this part, the tutorial demonstrates how to use ngClass within an ngRepeat directive. The example involves a table where different classes are applied to table rows based on the task.status property.

Example

<table>
    <tbody>
        <tr ng-repeat="task in todos" ng-class="{'warning': task.status == 'Hold', 'success': task.status == 'Completed', 'active': task.status == 'Started', 'danger': task.status == 'Pending'}">
            <td>{{$index + 1}}</td>
            <td>{{task.name}}</td>
            <td>{{task.date | date:'yyyy-MM-dd'}}</td>
            <td>{{task.status}}</td>
        </tr>
    </tbody>
</table>

Explanation:

• This code demonstrates using ngClass within an ngRepeat directive to conditionally style table rows based on the task.status property.
• Different classes are applied to the <tr> element based on the value of task.status.

Additional Techniques

This section introduces three additional techniques for using ngClass.

Using String Syntax

A simpler method using a shorthand if/else statement. The class applied depends on whether the expression is true or false.

<div class="{{expression == true ? 'class_if_expression_true' : 'class_if_expression_false' }}">Your Content</div>

Explanation:

• This code shows an alternative way to conditionally apply a class using string syntax and double curly braces ({{ }}).
• The class applied will be 'class_if_expression_true' if the expression is true, otherwise, it will be 'class_if_expression_false'.

Using Ternary Operator

It shows how to use the ternary operator within ngClass to conditionally apply one of two classes based on a variable or expression.

<div ng-class="$variableToEvaluate ? 'class-if-true' : 'class-if-false'"></div>

Explanation:

• This snippet introduces the ternary operator (? :) within ngClass.
• If $variableToEvaluate is truthy, 'class-if-true' will be applied; otherwise, 'class-if-false' will be applied.

Using Functions

This demonstrates how to use a function to determine the CSS class to be applied dynamically. It provides a code snippet showing how to define a function in the controller and use it within the ngClass directive.

JavaScript:

$scope.getCSSClass = function() {
    return "testclass";
}

Explanation:

• The JavaScript code defines a function getCSSClass in the controller, which returns the string 'testclass'.

HTML:

<div ng-class="getCSSClass()"></div>

Explanation:

• The ng-class directive then calls this function, and the returned value is used as the class to be applied dynamically.

Conclusion

The conclusion provides a summary of the tutorial, emphasizing the versatility of ngClass in dynamically styling elements based on changing conditions. It encourages further exploration of the discussed techniques for responsive and interactive styling in AngularJS applications.