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JavaScript addEventListener() with Examples

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  • Difficulty Level : Medium
  • Last Updated : 11 Jan, 2023
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Prerequisite: JavaScript events 

An event is an important part of JavaScript.A web page responds according to an event that occurred. Some events are user generated and some are generated by API. An event listener is a procedure in JavaScript that waits for an event to occur. A simple example of an event is a user clicking the mouse or pressing a key on the keyboard.

The addEventListener() is an inbuilt function in JavaScript which takes the event to listen for, and a second argument to be called whenever the described event gets fired. Any number of event handlers can be added to a single element without overwriting existing event handlers. 

Syntax: 

element.addEventListener(event, listener, useCapture);

Parameters:  

  • event: event can be any valid JavaScript event. Events are used without “on” prefixes like using “click” instead of “onclick” or “mousedown” instead of “onmousedown”.
  • listener(handler function) : It can be a JavaScript function that respond to the event occurring.
  • useCapture: It is an optional parameter used to control event propagation. A boolean value is passed where “true” denotes capturing phase and “false” denotes the bubbling phase.

Example 1:  In this example, we will display text on the webpage after clicking on the button.

HTML




<body>
    <button id="try">Click here</button>
    <h1 id="text"></h1>
    <script>
    document.getElementById("try").addEventListener("click", function(){
    document.getElementById("text").innerText = "GeeksforGeeks";
});
    </script>
</body>

Output: 

JavaScript addEventListener() with Examples

JavaScript addEventListener() with Examples

Example 2: In this example, two events “mouseover” and “mouseout” are added to the same element. If the text is hovered over then “mouseover” event occurs and the RespondMouseOver function is invoked, similarly for “mouseout” event RespondMouseOut function is invoked. 

HTML




<body>
    <button id="clickIt">Click here</button>
  
    <p id="hoverPara">Hover over this Text !</p>
  
  
    <b id="effect"></b>
  
    <script>
        const x = document.getElementById("clickIt");
        const y = document.getElementById("hoverPara");
          
        x.addEventListener("click", RespondClick);
        y.addEventListener("mouseover", RespondMouseOver);
        y.addEventListener("mouseout", RespondMouseOut);
          
        function RespondMouseOver() {
            document.getElementById("effect").innerHTML +=
                       "MouseOver Event" + "<br>";
        }
          
        function RespondMouseOut() {
            document.getElementById("effect").innerHTML +=
                      "MouseOut Event" + "<br>";
        }
          
        function RespondClick() {
            document.getElementById("effect").innerHTML +=
                      "Click Event" + "<br>";
        }
    </script>
</body>

Output: 

JavaScript addEventListener() with Examples

JavaScript addEventListener() with Examples

JavaScript is best known for web page development but it is also used in a variety of non-browser environments. You can learn JavaScript from the ground up by following this JavaScript Tutorial and JavaScript Examples.


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