Why preventDefault does not work?

Question

This is a part of my code. If I try to drop an image on the block preventDefault does not work.

        jQuery(document).ready(function($) {
            $.event.props.push('dataTransfer');
            $('#imgDropzone').on({
                dragenter: function(e) {
                    $(this).css('background-color', '#ffd1ff');
                },
                dragleave: function(e) {
                    $(this).css('background-color', '');
                },
                drop: function(e) {
                    e.stopPropagation();
                    e.preventDefault();

                    var file = e.dataTransfer.files[0];
                    var fileReader = new FileReader();
                    var el = $(this);
                    fileReader.onload = (function(file) {
                        return function(event) {
                            alert(event.target.result);
                        };
                    })(file);
                    fileReader.readAsDataURL(file);
                }
            });
        });

http://jsfiddle.net/LrmDw/

Answer 1

You need^* to prevent default for all the other drag events as well:

see http://jsfiddle.net/LrmDw/2/

$('#imgDropzone').on("dragenter dragstart dragend dragleave dragover drag drop", function (e) {
    e.preventDefault();
});

To explain what's not working in the original jsfiddle:

When you drop a file in the droparea (or anywhere in the page), the browser's default behavior is to navigate away and try to interpret the file. If you drop a normal txt file for example, the browser will navigate away from jsfiddle and display contents of the txt file. This is in Chrome.

---

Btw, base64 urls are not preferable since they duplicate data. Simply grab a blob pointer to the file and use that:

var file = e.dataTransfer.files[0];
var src = (window.URL || window.webkitURL).createObjectURL(file);
$("<img>", {src: src}).appendTo("body");

See

http://jsfiddle.net/LrmDw/3/

^{I don't know exactly which ones but I never had to care}