prints 1,2,3,4,5,6 using promises within a sequence

promise2.js

// serialize asynchronous code
// Start off with a promise that always resolves
var sequence = Promise.resolve();

// Loop 
[1,2,3,4,5,6].forEach(function(v) {
  // Add these actions to the end of the sequence
  sequence = sequence.then(function() {
    return new Promise(r => setTimeout(x => r(v), ((Math.random() * (10 - 1)) + 1 | 0) * 1000));
  }).then(v => console.log(v));
});

//or

[1,2,3,4,5,6].reduce(function(sequence, v) {
  // Add these actions to the end of the sequence
  sequence = sequence.then(function() {
    return new Promise(r => setTimeout(x => r(v), ((Math.random() * (10 - 1)) + 1 | 0) * 1000));
  }).then(v => console.log(v));
}, Promise.resolve());

inspired by: http://www.html5rocks.com/en/tutorials/es6/promises/#toc-parallelism-sequencing

very inefficient since the timeout is created within the sequence. see https://gist.github.com/ernestlv/7745b8c514f19a01f2b021e9064923ff