Introduction
One of the popular uses of Javascript is to add interactivity to web pages. These interactions could be functions that are triggered when an event occurs. For example, you might want to show a message to a user of your app when a button is used.
When building web apps with Javascript, however, you may encounter the need to remove or pause one or event more listeners that have been added to a particular element. A fine example of a case where an event listener might need to be removed is seen in a case where you need to perform a function when a button is clicked the first time only.
Intended Audience
This article is aimed at developers who have a basic understanding of web development and how event listeners can be added to HTML elements using Javascript.
Removing Event Listeners in JavaScript using the removeEventListener() method
In browsers that support modern JavaScript, the general syntax for removing event listeners is by making use of the removeEventListener() method as shown in the code block below.
element.removeEventListener("eventName", "functionName");
In the example code above, the element variable represents any element or a group of elements located in the DOM tree referenced using any query selector of your choice.
<body>
<h1>Hello User!</h1>
<button id="btn"> Show Message </button>
<p id="messageContainer"> </p>
</body>Next, let’s add a little bit of javascript to enable the button respond to the click event to display a given string message.
const button = document.getElementById('btn');
const messageContainer = document.getElementById('messageContainer');
const message = 'Hey, this is the message';
function showMessage(){
messageContainer.textContent = message;
}
button.addEventListener('click', showMessage)
Once we hit save and preview the code, the result displayed in the browser should be similar to the gif below.
How to remove event listeners In older browsers using JavaScript’s detachEvent() method
In some older browsers, particularly IE 8 and its predecessors, the removeEventListener() method would return as an undefined function. This behavior is because Internet Explorer (IE) versions 8 and lower do not provide support for the removeEventListener() method. Luckily, however, legacy javascript provides support for an alternative method to remove event listeners from elements using the detachEvent() method.
The general syntax for removing event listeners using the detachEvent() method can be seen in the code block below.
element.detachEvent("click", functionName)
If you need to remove event listeners in both old and new browsers, you can achieve this by combing both functions in an if statement using the example snippet below
const element = document.getElementById("elementId");
if (element.removeEventListener) {
// checks if removeEventListener is supported by the browser
element.removeEventListener("click", functionName);
} else if (element.detachEvent) {
// Falls Back to use detachEvent
element.detachEvent("click", functionName);
}Conclusion
Hopefully, reading this article should have given you a brief overview of what event listeners are and how they work in JavaScript, and how they can be easily removed if the need arises.
I’d love to hear in the comments if this article has helped with your knowledge of event listeners in Javascript. Keep on building awesome stuff! 🚀
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