Example of how to write a version of setTimeout that returns a promise

timeout-promise.js

function timeout(fn, delay) {
  var args = Array.prototype.slice(arguments, 2);
  
  return new Promise(function(resolve, reject) {
    setTimeout(function() {
      try {
        resolve(fn.apply(null, args));
      } catch(e) {
        reject(e);
      }
    }, delay);
  });
  
}