Fixing the preventDefault and return false Issues in JavaScript Form Validation

Learn why `preventDefault` and `return false` are not preventing form submission in your JavaScript code, and discover the correct way to handle form validation.
---

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: javascript return false or preventDefault is not working

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Understanding JavaScript Form Validation Issues

Requiring user input validation in forms is essential for any web application. Unfortunately, many developers encounter a frustrating issue where their JavaScript doesn't prevent the form from submitting as intended. In this post, we will explore the problem where the alert might show correctly but the subsequent form submission still occurs. We'll analyze the code provided, identify the issues, and present a clear solution.

The Problem at Hand

You've likely experienced this scenario: despite having validation logic in place, such as using preventDefault() or returning false, the form still submits. In the code snippet shared:

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

In this function, you try to catch a bad email format using a regular expression. While your alert appears as expected, the form continues to submit once you click "OK." This indicates that something is wrong with your approach.

Why Is This Happening?

Explanation

preventDefault() Usage: This method is called on events (like form submissions), but in your code, it's being called on the inputText element, which does not have a preventDefault method.

Returning false: While you correctly tried using return false, the context in which it's used is crucial. If this return statement is located within a function that's not directly tied to the form submission event, it won't work as intended.

The Right Approach

Instead of attaching your validation logic to the onclick event of the button, you should have it in the onsubmit event of the form itself. Here's how to do it:

Step-by-Step Solution

1. Move the Validation to the Form's onsubmit Event

You'll have to attach your function directly to the form, as shown below:

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

2. Update the Validation Function

Next, adjust the function to return false in case of invalid input:

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

Conclusion

Implementing form validation can be tricky if the event handling and return flow aren't set up correctly. By placing your validation logic within the onsubmit event of the form, you ensure that the form submission is only allowed when the input is valid. With these adjustments, your validation should work seamlessly, preventing unwanted submissions.

Key Takeaway

Always ensure that validation is handled in the onsubmit event of the form—not the onclick event of an input. This small change can make a significant difference in the performance of your form validation. Happy coding!