Issue with Firefox: During drag events, dataTransfer.files return as null, while this behavior is consistent in all other browsers

Take a look at this jsfiddle to see the exact issue in action.

In my experience, the 'dragenter' event dataTransfer.files works correctly in all browsers except for Firefox. However, I have noticed that the 'drop' event consistently provides the correct dataTransfer.files even in Firefox.

I'm not sure if this is a potential bug specific to Firefox (versions 21.0 and 23.0.1) as I have encountered this on both Mac OS and Windows platforms.

Below is the full code snippet:

function preventDefault(_e) {
    _e.preventDefault();
}

var dropZone = document.getElementById('drop-zone');
dropZone.addEventListener("dragstart", preventDefault, false);
dropZone.addEventListener("dragleave", preventDefault, false);
dropZone.addEventListener("drag", preventDefault, false);
dropZone.addEventListener("dragend", preventDefault, false);
dropZone.addEventListener("dragover", preventDefault, false);
dropZone.addEventListener("dragenter", function(_e) {
    _e.preventDefault();
    console.log(_e.dataTransfer.files);
}, false);
dropZone.addEventListener("drop", function(_e) {
    _e.preventDefault();
    console.log(_e.dataTransfer.files);
}, false);

Have others experienced similar issues?

It's possible that this could be due to sandbox restrictions, although I haven't come across any information confirming this...

Your thoughts and insights are welcomed :).

Answer №1

Based on the specifications from W3C and WhatWG, it appears that data is in "Protected mode", making it inaccessible. This feature likely aims to prevent unauthorized access and theft of information during drag and drop operations.

This suggests that Firefox's decision to restrict access to .files during dragenter events is correct, implying that the issue lies with other browsers allowing such access.

In fact, the source code for Firefox explicitly shows no data being returned during a dragenter event.

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