How run async / await in parallel in Javascript

Question

Finally async/await will be supported in all major browser soon except IE. So now we can start writing more readable code with async/<

Answer 1

For those asking how you extend this to a run-time determined number of calls, you can use 2 loops. The first starts all the tasks, the second waits for everything to finish

console.clear();

function wait(ms, data) {
  return new Promise( resolve => setTimeout(resolve.bind(this, data), ms) );
}

/** 
 * While here we call the functions first,
 * then wait for the result later, so 
 * this will finish in 500ms.
 */
async function runTasks(timings) {
  let tasks = [];
  for (let i in timings) {
      tasks.push(wait(timings[i], `Result of task ${i}`));
  }

  /* Want fast fail? use Promise.All */
  //return Promise.All(tasks);
  
  let results = [];
  for (let task of tasks) {
       results.push(await task);
  }

  return results;
}

async function taskRunner(fn, arg, label) {
  const startTime = performance.now();
  console.log(`Task ${label} starting...`);
  let result = await fn(arg);
  console.log(`Task ${label} finished in ${ Number.parseInt(performance.now() - startTime) } miliseconds with,`, result);
}

void taskRunner(runTasks, [50,100,200,60,500], 'Task List');