FileReader error: The object is already busy reading Blobs

Question

I\'m making a drag-and-drop file upload system for photo gallery uploads. This is my source code handling dropped files. This one works multiple files if I drop them one by one

Answer 1

A case that can cause this is when a file reader gets called twice. If it's still running, it will issue this error.

    reader.onload = function( event ) {
            // do stuff
        };
    reader.readAsDataURL( file );

    /* arbitrarily complex code */
    reader.readAsDataURL( file2 );

    /* oops */