FileReader.readAsArrayBuffer return is null

Question

I am following Html5rocks tutorial

http://www.html5rocks.com/en/tutorials/file/dndfiles/

and I am trying to use readAsArrayBuffer instead of readAsBinaryString in slicing a file example (because I want to read gif header to find file resolution). But I am stuck because evt.target.result (while using readAsBinaryString it is a string)

any ideas?

EDIT : Code

reader.onloadend = function(evt) 

{

  if (evt.target.readyState == FileReader.DONE) { // DONE == 2
    document.getElementById('byte_content').textContent = evt.target.result;
    console.log(evt.target.result.byteLenght)
    document.getElementById('byte_range').textContent = 
        ['Read bytes: ', start + 1, ' - ', stop + 1,
         ' of ', file.size, ' byte file'].join('');
  }
};

if (file.webkitSlice) {
  var blob = file.webkitSlice(start, stop + 1);
} else if (file.mozSlice) {
  var blob = file.mozSlice(start, stop + 1);
}
reader.readAsArrayBuffer(blob);
}

so in Firefox 13 I get on screen : [object ArrayBuffer]

and on console log : undefined

while in Chromium 18 I get on console : Uncaught TypeError: Cannot read property 'byteLenght' of null

Where exactely are you stuck? this is the base code. Now, what are your modifications, what did you expect and what goes wrong? — Rob W
– Rob W, Commented Jun 18, 2012 at 20:46
@RobW I changed reader.readAsBinaryString(blob); to eader.readAsArrayBuffer(blob) and I was expecting to get ArrayBufferbut I get null. — wonglik
– wonglik, Commented Jun 18, 2012 at 20:51
Can't reproduce in Chromium 18: jsfiddle.net/XDbnJ I see [object arrayBuffer]. Include your code in the question, including details about your browser and your expectations. — Rob W
– Rob W, Commented Jun 18, 2012 at 20:57
I can still not reproduce the error: jsfiddle.net/XDbnJ/1. Also, byteLength has to be spelled with th, not ht. Post a full demo using jsfiddle.net whihc shows your problem. — Rob W
– Rob W, Commented Jun 18, 2012 at 22:01

Thiem Nguyen · Accepted Answer · 2012-06-22 16:58:35Z

5

There is a typing mistake in:

console.log(evt.target.result.byteLenght)

byteLenght should be byteLength

edited Jun 22, 2012 at 16:58

Thiem Nguyen

6,3657 gold badges33 silver badges50 bronze badges

answered Jun 22, 2012 at 6:05

colxi

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1 Comment

Rob W Over a year ago

I already mentioned that in the comments. This is not the cause of the problem though: This would just log undefined, and not throw a TypeError.

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