How Can I Verify File Size Before Uploading Using JavaScript?

Verifying File Size in JavaScript Before Upload

File size validation is crucial to prevent uploading excessive files that might overload servers or consume excessive storage space. Fortunately, JavaScript offers methods to check file size before initiating an upload.

Using File API for Size Validation

The File API provides a seamless way to analyze and validate files in JavaScript. To leverage its capabilities, follow these steps:

1. Check Browser Compatibility: Verify that the File API is supported in the targeted browser (it's widely supported).
2. Retrieve File: Use the files property of file input elements to access the selected file.
3. Obtain File Size: The size property of the retrieved file object provides the file size in bytes.

Here's a practical example that demonstrates the process:

<form action="#" onsubmit="return false;">
    <input type="file">

This script effectively displays the size of the selected file in a friendly message, allowing users to confirm if they wish to proceed with the upload.

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