using promise.all code example

Example 1: javascript promise.all

try {
    const [res1, res2, res3] = await Promise.all([
      Promise1,
      Promise2,
      Promise3,
    ]);
  } catch (err) {
    console.error(err);
  }

Example 2: javascript promise.all

// PARALLEL PROMISES
async function fetchMoviesAndCategories() {
  const [moviesResponse, categoriesResponse] = await Promise.all([
    fetch('/movies'),
    fetch('/categories')
  ]);

  const movies = await moviesResponse.json();
  const categories = await categoriesResponse.json();

  return [movies, categories];
}

Example 3: promise all in promise all

var arr = [
  {subarr: [1,2,3]},
  {subarr: [4,5,6]},
  {subarr: [7,8,9]}
];
function processAsync(n) {
  return new Promise(function(resolve) {
    setTimeout(
      function() { resolve(n * n); },
      Math.random() * 1e3
    );
  });
}
Promise.all(arr.map(function(entity){
  return Promise.all(entity.subarr.map(function(item){
    return processAsync(item);
  }));
})).then(function(data) {
  console.log(data);
});