Read and base64 encode a binary file

I'm trying to read a binary file from the filesystem and then base64 encode it in JavaScript. I'm using the FileReader API to read the data and the base64 encoder found here.

The code I have seems close to working, the problem is that the generated base64 data is wrong. Here's what I've got so far:

function saveResource() {
    var file = $(".resourceFile")[0].files[0];

    var reader = new FileReader();
    reader.onload = function(evt) {
        var fileData = evt.target.result;
        var bytes = new Uint8Array(fileData);
        var binaryText = '';

        for (var index = 0; index < bytes.byteLength; index++) {
            binaryText += String.fromCharCode( bytes[index] );
        }

        console.log(Base64.encode(binaryText));

    };
    reader.readAsArrayBuffer(file);
};

Here's the file I'm testing with (it's a 100x100 blue square):

According to an online base64 decoder/encoder, this file should encode to:

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