Runs a function in a web worker

usage.md

Make sure the Content Security Policy allows access to scripts that have been created on the same origin (eg: this will not work in the gists developer console since script-src is set to assets-cdn.github.com)

function sum(arr) {
    return arr.reduce(function(a, b) { return a + b; });
}

var sumWorker = workerFn(sum);

// generate input
for(var input = []; input.length < 1000; input.push(input.length));

sumWorker(input).then(function(result) { console.log(result); });   

workerFn.js

function workerFn(fn) {
  return function () {
    var args = [].slice.call(arguments);

    return new Promise(function (resolve, reject) {
      // wrap function in onmessage/postMessage 
      var workerScript = 'self.onmessage = function(e) {' +
        'postMessage((' + fn.toString() + ').apply(null, e.data));' +
        'self.close();' + 
      '}';

      // create worker from object url
      var objectUrl = URL.createObjectURL(new Blob([workerScript]));
      var worker = new Worker(objectUrl);

      worker.onmessage = function(e) { 
        URL.revokeObjectURL(objectUrl);
        resolve(e.data); 
      };

      worker.onerror = function(e) { 
        URL.revokeObjectURL(objectUrl);
        reject(e); 
      };

      worker.postMessage(args);
    });
  }
}