How Can I Efficiently Check if a JavaScript DOM Element Contains a Specific Class?

Checking if an Element Contains a Class in JavaScript

In JavaScript, you may encounter scenarios where you need to determine if a DOM element contains a specific class. Although your current approach using element.className and a switch statement can work, it has limitations when an element has multiple classes.

Using element.classList.contains()

For better cross-browser compatibility, you can utilize the element.classList.contains() method:

element.classList.contains(className);

This method returns a boolean indicating whether the element has the specified class. It is supported in all major browsers.

Alternative Approach with indexOf

If you're dealing with legacy browsers that don't support element.classList, you can modify your existing indexOf approach as follows:

function hasClass(element, className) {
    return (' ' + element.className + ' ').indexOf(' ' + className+ ' ') > -1;
}

This ensures that the check only returns true if the class you are looking for is not contained within another class name.

Example Implementation

Applying the updated techniques to your example:

var test = document.getElementById("test"),
    classes = ['class1', 'class2', 'class3', 'class4'];

test.innerHTML = "";

for(var i = 0, j = classes.length; i < j; i++) {
    if(hasClass(test, classes[i])) {
        test.innerHTML = "I have " + classes[i];
        break;
    }
}

This approach handles the case where the test element has multiple classes, ensuring that the correct class is detected even if its order or additional classes are present.

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