Run promises as sequence

promise-sequence.js

function sequence(promises) {
  return new Promise((resolve, reject) => {
    const rets = []
    const gen = (function*() {
        // loop as long as we have promises in the queue
        while (promises.length) {
          // take always the first promise
          const promise = promises.shift()
            // wait until it's resolved to step to the next iteration
          promise
            .then(gen.next.bind(gen))
            .catch(reject)
            // push the result to the return values
          rets.push(yield)
        }
        // resolve the promise with all the returned values if everything went fine
        resolve(rets)
      })()
      // kick the generator
    gen.next()
  })
}

sequence([
  new Promise(r => setTimeout(r, 2000, 'ciao')),
  new Promise(r => setTimeout(r, 1000, 'bello')),
]).then(console.log).catch(console.log)