How to Assign the Same Function to Multiple HTML Elements in JavaScript

Discover how to effectively assign the same JavaScript function to multiple buttons on different HTML pages and ensure they work seamlessly.
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How to Assign the Same Function to Multiple HTML Elements in JavaScript

In the world of web development, you may encounter scenarios where you want multiple buttons or elements to perform the same action when clicked. A common question arises when one button works while another seemingly does not, even though they are set to run the same JavaScript function. This guide will address that question and provide a clear solution.

The Problem

You have two buttons on different HTML pages, # Button1 and # Button2, and you have assigned them the same click event handler in JavaScript, like so:

[[See Video to Reveal this Text or Code Snippet]]

Here, you noticed that one button works while the other does not. Upon switching their order, the opposite button starts to function while the previously functional one fails. This issue typically arises due to the elements not being available in the DOM when trying to assign the event handlers.

Understanding the Issue

The problem is mainly caused by the timing of when the elements are being queried. When the JavaScript runs, if one of the buttons does not exist on the current page, the querySelector will return null, leading to a failure when trying to assign the onclick event.

Key Points to Consider:

Element Availability: The buttons may not exist at the time your script is running.

Separate HTML Pages: If buttons are on different pages, you'll need a way to check if they exist before assigning events.

The Solution

To ensure that both buttons work regardless of them being present on various HTML pages, you can modify your script to check for the existence of each button before trying to assign the function. Here’s how you can do it:

[[See Video to Reveal this Text or Code Snippet]]

Breakdown of the Solution:

Using DOMContentLoaded: The event ensures that your JavaScript runs only after the HTML is fully loaded.

Checking for Element Existence:

The script checks if # Button1 exists:

If it does, the function fun gets assigned to its onclick.

The same check is done for # Button2.

Assigning the Function: If the button exists, the click event is assigned, ensuring no errors will be thrown for non-existent elements.

Conclusion

By checking for the existence of the elements # Button1 and # Button2 before assigning event handlers, you create a robust JavaScript solution that can work seamlessly across different HTML pages. This method will prevent errors when buttons are missing while maintaining functionality when they are present.

Feel free to implement this change in your code, and watch as both buttons respond to clicks as intended!