javascript - HTML5 File API crashes Chrome when using readAsDataURL to load a selected image

Question

Here's my sample code:

var input = document.createElement('input');
input.type = 'file';
document.body.appendChild(input);

input.addEventListener('change', function(){
    var file = input.files[0];

    var reader = new FileReader();
    reader.onload = function(e){
        var image = new Image();
        image.src = e.target.result;
    };
    reader.readAsDataURL(file);
});

Load the page, select a large image (I'm using a 2.9MB 4288x3216 image). Refresh the page and select the same image. Result? The tab crashes! (Aw, Snap!)

My guess is that this is a bug with Chrome's implementation of the File API, but I'd love it if someone could confirm that and maybe even offer a workaround. I really want to be able to show a thumbnail of a photo without having to go to the server to generate one (even if it's just for Chrome and FF).

Also, with my sample code above, as soon as you select the photo, the tab starts using about 32MB more of memory. That, I guess, is expected, but what concerns me is that the memory never seems to get freed by the garbage collector. So if I keep selecting more photos, I keep consuming more memory. I don't know if this is related to the crashing issue or not, but it's definitely a concern.

Thanks for any help!

Answer 1

The memory issue could be a result of this bug: http://crbug.com/36142. Essentially, Chrome is caches data: URLs and currently does not release the memory when the img.src is changed. The other issue is that data: URLs yield a 33% overhead to the data you're encoding. That means you're actually setting a ~3.85MB resource on the image, not 2.9MB.

Since you're not manipulating the content (the actual bytes), there's no need to read the file content. One option is to create a blob: url. There's also an explicit revoke method, so you won't run into the same memory caching issues. Something like:

input.addEventListener('change', function(e) {
  var file = input.files[0];

  window.URL = window.webkitURL || window.URL; // Vendor prefixed in Chrome.

  var img = document.createElement('img');
  img.onload = function(e) {
    window.URL.revokeObjectURL(img.src); // Clean up after yourself.
  };
  img.src = window.URL.createObjectURL(file);
  document.body.appendChild(img);
});