Javascript Events

Code Snippets Events
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About

In this code snippet, we’ll learn about events in Javascript.

We can add and subsequently remove event listeners(of different types: click, change, mouseenter, …) to any element of our choosing. These event listeners will wait for the specified event(like clicking on an element) to occur. When finally it does the event listener will call/execute the code we specified beforehand.  

Let’s see the code example below.

Code:

index.html
<!DOCTYPE html>
<html>
    <head>
        <title>DOM Manipulation</title>
    </head>
    <script src="code.js"></script>
    <script>
        function sayThanks(){
            alert("Thanks.");
        }
    </script>
    <body>
        <div>
            <div style="background-color: blue; width: 100px; height: 100px;"></div>
            <! – Events can also be registered like so(but the function must be defined in this file!): – >
            <h1 onclick="sayThanks()">Please click me.</h1>
            <h1 onclick="this.innerHTML = 'Thanks.'">Please click me.</h1>
        </div>
    </body>
</html>
code.js
//Run this when the HTML gets loaded.
window.onload = () => {

    //Add event listener. //Possible events: "click", "mouseenter", "mouseleave", "change", "keydown", "load"
    document.getElementById("coloredDiv").addEventListener("click", changeColor);
    
    //Remove event listener.
    //document.getElementById("coloredDiv").removeEventListener("click", changeColor);

    function changeColor(eventArgs){
        //eventArgs.currentTarget will return the element that was clicked.
        //Then we can simply use .style.backgroundColor to change its color.
        eventArgs.currentTarget.style.backgroundColor = "red";
    }
}

Resulting output:

Before:
After:
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