[JavaScript] Understanding Onclick() Event Listener

Introduction

This article explores two ways of adding an event listener onclick().

Adding onclick="" property in your HTML tag.
Using addEventListener() method in JavaScript.

[JavaScript] Accessing the DOM Using JavaScript - Explained with Examples.

Onclick Property in HTML Tag

Onclick property is written in your HTML tag, and receives the function after the assignment operator(=).

That function is executed when the user clicks a button.

Before going through this article, if you don't know how to access the DOM(document object model), check out this article.

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <button onclick="doSave();" id="btn">Save</button>
  </body>
    <script>
        function doSave() {
            // code in here will be executed when the user clicks a button
        }
    </script>
</html>

Using addEventListener Method in JavaScript

You can use an addEventListener method to do the same task as above.

I prefer using this, and many developers also prefer to do this because your code is more manageable and readable.

Imagine you have a thousand lines of HTML code. It would be quite hard to manage them. So, we can create a function in JavaScript to make it more manageable.

AddEventListener receives two parameters:

Event type
Function that will be executed when the event happens.

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <button id="btn">Save</button>
  </body>
    <script>
        function addClickEvent() {
            document.querySelector("#btn")
            .addEventListener("click", function() {
                // code in here will be executed when the user clicks a button
            }
        }
    </script>
</html>

What the function addClickEvent() is doing:

Access the DOM by using the id="btn".
Specifies that the event listener "click" is added.
When a user clicks a button, anything inside the function (second parameter of addEventListener) will be executed.

[JavaScript] Understanding Onclick Event Listener and Various Ways to Code It.

Table of contents

Introduction

Onclick Property in HTML Tag

Using addEventListener Method in JavaScript

Subscribe to my newsletter

Lim Woojae

Lim Woojae