Understanding Why Your onclick Button Calls a Function on Page Load

Learn how to fix the issue of your button calling a function when the page loads instead of on click. Explore the solution using NodeJS with Express and EJS.
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Understanding Why Your onclick Button Calls a Function on Page Load

When developing web applications, it's common to encounter unexpected behavior in our JavaScript functions. One such issue that can be particularly perplexing is when an onclick button appears to call a function upon page load rather than in response to user interaction. If you’ve found yourself troubleshooting this frustrating problem, don’t worry; you’re in the right place! In this guide, we’ll explore the root of the issue and present a clear solution so you can get your button functioning as intended.

The Problem Explained

What’s Happening?

You are working within a NodeJS environment using Express and EJS, and you’ve encountered a scenario where your button unexpectedly triggers a function when the page loads. Here’s a simplified breakdown of your implementation:

You are trying to execute a function defined in your JavaScript helper when a button is clicked using the following code:

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

However, the button is calling the function as soon as the page loads, not when you click it. This behavior occurs because of how EJS interprets the code.

Understanding EJS Usage

In EJS, when you use <% %>, it treats the content as server-side code, executing it during the rendering of the page before it reaches the client. This means that the helper.test() function executes immediately rather than waiting for a click event.

The Solution: Setting Up HTTP Endpoints

Step 1: Define an HTTP Endpoint

To resolve this issue, you need to establish a way for your client-side code to communicate with your server. Here’s how you can do that:

Create an Express Route: Define an endpoint in your server code that will invoke the helper.test() function when requested. Here’s how to do it:

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

This code sets up a route at /helper_test, which, when accessed, will run helper.test().

Step 2: Update Your Client-Side Code

Next, you should modify your button in the EJS file and use an event handler that calls this new endpoint when clicked. Here’s an updated version of your button:

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

Explanation of the New Code

Button Click: The button now calls a JavaScript function callHelperTest() when clicked.

Fetch API: Inside callHelperTest, the fetch() function is used to send a request to the /helper_test endpoint you defined. The function helper.test() on the server will execute upon receiving this request.

Conclusion

By setting up an HTTP endpoint and modifying your button to call a JavaScript function, you can effectively control when your helper.test() function executes—only responding to user interaction. This approach ensures that your client-side interacts correctly with your server without execution errors and unwanted behavior.

If you’ve encountered this issue before, you now have a clear path to troubleshoot it. Remember, understanding the separation between client and server processes and utilizing HTTP requests is key to solving similar problems in web development. Happy coding!