Node: Process a 2D array of promises

Question

I have a 2D array (2 X n) of promises and I want first to process all the promises in Row 1 and then all the promises in Row 2.

In other words, I want to chain one group of promises after another group of promises completes its execution.

How can I achieve this?

I tried the following but it doesn't work. Any ideas?

 Promise.resolve()
    .then(createPromises)//generates topPromises= [ [p1, p2, p3], [p4,p5,p6]]
    .then(function(topPromises){
      Promise.all(topPromises[0])
      .then(Promise.all[topPromises[1])
    })

Answer 1

You can pull this off using a little bit of pseudo-recursion.

Essentially, you have a function which completes one group of promises. Once it completes, you call that same function again but with the next group.

let promiseCount = 1;
function create() {
  let n = promiseCount++;
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      console.log(n);
      resolve();
    }, 500 * n);
  });
}

let groups = [
  [create(), create(), create()],
  [create(), create(), create()],
  [create(), create(), create()]
];

(function runGroup(i) {
  if (i < groups.length) {
    Promise.all(groups[i])
      .then(() => {
        console.log('Group', i + 1, 'complete');
        runGroup(i + 1);
      });
  }
})(0);