// Created on savesnippets.com · https://savesnippets.com/ME3ekxwhqAQHLg
function createQueue() {
  let tail = Promise.resolve();
  return {
    add(task) {
      const result = tail.then(() => task());
      tail = result.catch(() => {}); // keep queue running on error
      return result;
    },
  };
}

// Usage
const q = createQueue();

q.add(() => fetch('/api/step1').then((r) => r.json())).then(console.log);
q.add(() => fetch('/api/step2').then((r) => r.json())).then(console.log);
// step2 only starts after step1 finishes