Validate file size in Javascript / jQuery

Sometimes you need some rather basic validation of file size. I had to write this for a project recently, where I needed to check the file size prior to upload.

After doing some digging around I came up with a cross browser solution (Safri, IE, Chrome, Firefox) that works quite well. In my example, I'm ensuring an image is no greater than 6MB in binary size.

function validate_file_size(elem, max_bytes, callback) {
    var img = new Image();
    var _URL = window.URL || window.webkitURL;
    img.src = _URL.createObjectURL(elem);
    return img.onload = function() {
        if (typeof elem == 'object' && typeof elem['size'] != 'undefined') {
            if (elem.size <= max_bytes) { // Max file size.
                return callback(true);
            }
        }
        return callback(false);
    };
}

Now, to use this it's quite simple.

$('#fileOne input[type="file"]').on('change', function (e) {
    var file = $(this)[0].files[0];
    validate_file_size(
        file,
        6291456,
        function(result){
            if (!result) {
                alert('The maximum file size allowed is 6 MB.');
                return;
            }
            setTimeout(function () {
                showLoad();
                $('#fileOne input[type="submit"]').click();
            }, 200);
        }
    );
});