HTML5 File API: FileReader.readAsText() returns "undefined"

Question

I use Chrome 12 on Mac OS X and I've included jQuery 1.6.1 within the document.

I try to read the contents of a file as text and save it in a data-object with the following function:

this.upload = function(file) {
    console.log('FileHandler.upload called with ' + file.name + '.');
    console.log(file);
    console.log(this.reader);

    data = {
        content: this.reader.readAsText(file)
    }

    console.log('Content: ' + data.content);
}

"file" seams to be a valid file-object and "this.reader" is a fresh instance of type FileReader. This code creates the following console output:

http://cl.ly/1Y2b383G2F272x1m1P0N

enter image description here

pimvdb · Accepted Answer · 2011-06-20 18:34:00Z

16

That's not the way it works according to the docs. You should call the readAsText() function, and when it's completed the result is stored in .result.

answered Jun 20, 2011 at 18:34

pimvdb

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Matthew Holder · Accepted Answer · 2022-03-07 18:50:44Z

0

i found this example in this page of the docs and it worked for me on the first try:

HTML:

<input type="file" onchange="previewFile()"><br>
<p class="content"></p>

JavaScript:

function previewFile() {
  const content = document.querySelector('.content');
  const [file] = document.querySelector('input[type=file]').files;
  const reader = new FileReader();

  reader.addEventListener("load", () => {
    // this will then display a text file
    content.innerText = reader.result;
  }, false);

  if (file) {
    reader.readAsText(file);
  }
}

answered Mar 7, 2022 at 18:50

Matthew Holder

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