worker.js

"use strict";
self.onmessage = function(e) {
  if (e.data.ib === true) {
    postMessage({bin: e.data.f.slice(e.data.cs * (e.data.cc - 1), e.data.cs * e.data.cc), chunkId: e.data.cc});
  } else {
    var fileReader;
    if (self.FileReader) {
      fileReader = new FileReader();
      fileReader.onloadend = function(chunk) {
        postMessage({bin: (fileReader.result || chunk.srcElement || chunk.target).split(',')[1], chunkId: e.data.cc, s: e.data.s});
      };

      fileReader.onerror = function(error) {
        throw (error.target || error.srcElement).error;
      };

      fileReader.readAsDataURL(e.data.f.slice(e.data.cs * (e.data.cc - 1), e.data.cs * e.data.cc));

    } else if (self.FileReaderSync) {
      fileReader = new FileReaderSync();
      postMessage({bin: fileReader.readAsDataURL(e.data.f.slice(e.data.cs * (e.data.cc - 1), e.data.cs * e.data.cc)).split(',')[1], chunkId: e.data.cc});

    } else {
      postMessage({bin: null, chunkId: e.data.cc, error: 'File API is not supported in WebWorker!'});
    }
  }
  return;
};