Stagger execution of a for loop

forloop_stagger.js

const items = [1, 2, 3, 4, 5];

let promise = Promise.resolve();
for (let i = 0; i < items.length; i++) {
  promise = promise.then(() => {
    console.log(items[i]);
    return new Promise((resolve) => {
      setTimeout(resolve, 500);
    });
  });
}

const items = [1, 2, 3, 4, 5];

let promise = Promise.resolve();
for (let i = 0; i < items.length; i++) {
  setTimeout(() => console.log(items[i]), 2000);
}

Instead of printing out the next iteration of the loop every 2 seconds, the above will add the callback function to the event queue to be called at a later time. This means that all items in the index will be printed out 2 (or so) seconds later. If we want to accomplish functionality that prints each iteration of the loop with a 2 second gap in between each print line, we can use promises to wait on the each execution of the loop.