UTF-16 byte array from file in javascript?

Question

I have a file that's encoded with UTF-16 and the encoded string has characters such as à and ÷. The code I use to read the file is:

  var reader = new FileReader();
  reader.readAsArrayBuffer(real_file_button.files[0]);
  reader.onloadend = function (evt) {
      if (evt.target.readyState == FileReader.DONE) {
         var arrayBuffer = evt.target.result,
             array = new Uint8Array(arrayBuffer);
         for (var i = 0; i < array.length; i++) {
             fileByteArray.push(array[i]);
          }
      }
  }

but since it is reading it as UTF-8 the à and ÷ characters get converted to �. How can I get a byte array of the file while keeping the correct encoding?

"but since it is reading it as UTF-8" - um, no? It is reading the file into a raw buffer of bytes, there are no strings and no encoding involved in the code you've shown. Where exactly do you output any characters? — Bergi
– Bergi, Commented Nov 21, 2019 at 1:04
Btw, what is fileByteArray, what's the point of copying the array you already have into it? — Bergi
– Bergi, Commented Nov 21, 2019 at 1:05

Kaiido · Accepted Answer · 2019-11-21 00:45:15Z

2

There is nothing doing any conversion to UTF-8 here, you are just copying the numerical values from the TypedArray view to a normal Array (which seems quite pointless btw...).

Not sure what you call a "byte array", but if you want to read this binary data as an UTF-16 string, then use the readAsText( blob, encoding ) method of the FileReader:

const file = real_file_button.files[0];
reader.onload = (e) => doSomethingWith( reader.result );
reader.readAsText( file, "utf-16" )

This will default to little endian utf-16. If you need big endian, use "utf-16be".

If you wish to view your ArrayBuffer as uint16 values, then create an Uint16Array view of it:

reader.readAsArrayBuffer( file );
reader.onload = (e) => {
  const uint16view = new Uint16Array( reader.result );
  // doSomethingWith( uint16view )
};

edited Nov 21, 2019 at 0:45

answered Nov 20, 2019 at 23:57

Kaiido

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