How to handle errors in JavaScript drag and drop functionality

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1

I’m working on a drag and drop feature for file uploads and running into an issue. When users try to drop files on Windows 10, sometimes the files just vanish without any error message.

After some testing, I found out this happens when the file path plus filename exceeds 1000 characters. Files with shorter paths work perfectly fine. I think this is related to the DataTransferItem character limit.

I want to show users a helpful error message when this happens instead of files just disappearing. Is there a way to detect and catch these kinds of errors in drag and drop operations?

Here’s my current setup:

fileDropZone.addEventListener('dragover', handleDragOver);
fileDropZone.addEventListener('dragenter', handleDragEnter);
fileDropZone.addEventListener('dragleave', handleDragLeave);
fileDropZone.addEventListener('dragend', handleDragEnd);
fileDropZone.addEventListener('drop', processDroppedFiles);

function processDroppedFiles(event) {
   const fileList = event.dataTransfer.items;
   console.log(fileList);
}

Any suggestions on how to catch these errors and provide better user feedback?

2

Had the same problem building a file sharing tool. Windows filesystem limits don’t just affect path length - they mess with how DataTransfer handles certain file types and locations too. Here’s what fixed it for me: set a timeout after the drop event to check if all files actually made it through. If the count doesn’t match what got dropped, something failed silently. I also check DataTransfer.files.length right away, then again after a short delay. When files disappear, the length usually changes between these checks. Another trick - look at file.lastModified timestamps. Corrupted transfers often have bogus dates. Using both methods catches most silent failures so you can show users actual error messages about file problems.

3

same issue here, but only on chrome. the DataTransfer API silently craps out with long file paths. check event.dataTransfer.types first - when it breaks, the types array goes empty or gets corrupted. i wrap my file reading in a promise with timeout too. if it’s taking forever, something’s wrong. fixed most of my edge cases.

4

I hit this exact issue building a document management system last year. Windows has path length restrictions that mess with the DataTransfer API. Here’s what fixed it for me: validate files right after accessing the dropped items, don’t wait for DataTransfer to catch it. Check the file properties directly - when a file exceeds the path limit, the File object gets weird. Sometimes the name gets truncated or size shows zero even though it’s a valid file. Wrap your file processing in try-catch and validate each file object before reading it. I also check if file.name exists and isn’t crazy long - helps catch these problem drops. Then you can show users a proper error message telling them to shorten the path or rename files. Works reliably across different Windows versions.