.md

[FIXED]: File Input Not Triggering onChange When Re-Selecting the Same File

Introduction

While working with file uploads in React, you may encounter an issue where selecting a file, modifying it from file explorer, and then picking it again does not trigger the onChange event. This can be frustrating, especially when handling file validation or re-uploads. The root cause is that browsers do not fire onChange if the same file (by name) is selected again.

The Problem

Let's consider a common React file input implementation:

<input type="file" onChange={(e) => handleFileUpload(e.target.files[0])} />

At first, everything works fine:

1. A user selects document.pdf, and the onChange event fires.
2. The file is uploaded, but the server rejects it due to invalid content.
3. The user modifies document.pdf and selects it again.
4. Nothing happens! The onChange event does not trigger.

Why Does This Happen?

Browsers optimize file inputs by not triggering onChange if the selected file has the same name and path as the previous selection. Since document.pdf remains the same filename, the event does not fire, causing the issue.

The Fix: Resetting Input Value

To ensure the onChange event fires even when selecting the same file, we can reset the input field on click:

<input 
  type="file" 
  onClick={(e) => (e.target.value = null)}
  onChange={(e) => handleFileUpload(e.target.files[0])} 
/>

How This Fix Works

• The onClick event resets the input value before selecting the file again (e.target.value = null), ensuring that even if the user selects the same file, the onChange event will trigger.
• The onChange handler then properly processes the newly selected file.

Alternative Fix: Resetting on Change

Another way to solve this is by resetting the value inside onChange:

<input
  type="file"
  onChange={(e) => {
    if (!e.target.files.length) return;
    handleFileUpload(e.target.files[0]);
    e.target.value = ""; // Reset after handling file
  }}
/>

Axios Network Error Caused by This Issue

If you are using Axios for file uploads, this issue can also cause a misleading Network Error.  This could be due to React state still holding a reference to the previously selected file, which has already been modified. Axios may not receive the correct file reference, leading to an error response.

Example error message:

{
  "message": "Network Error",
  "name": "AxiosError",
  "stack": "AxiosError: Network Error at XMLHttpRequest.handleError...",
  "config": {...},
  "code": "ERR_NETWORK"
}

Conclusion

If you're dealing with file uploads in React (or vanilla JavaScript) and notice that selecting the same file twice doesn't trigger onChange, resetting the input field value is a simple and effective fix. Adding e.target.value = null to onClick ensures smooth re-selection and prevents unexpected behavior in file upload forms. Additionally, this fix can help prevent Axios network errors caused by stale file references in state.

Happy coding! 🚀