Answer

Promise.allSettled() waits until all input promises have settled, whether fulfilled or rejected. It returns an array describing each outcome in the same order as the input.

if (!Promise.myAllSettled) {
  Promise.myAllSettled = function (iterable) {
    return new Promise((resolve, reject) => {
      let items;

      try {
        items = Array.from(iterable);
      } catch (error) {
        reject(error);
        return;
      }

      if (items.length === 0) {
        resolve([]);
        return;
      }

      const results = new Array(items.length);
      let remaining = items.length;

      items.forEach((item, index) => {
        Promise.resolve(item).then(
          value => {
            results[index] = {
              status: "fulfilled",
              value
            };
          },
          reason => {
            results[index] = {
              status: "rejected",
              reason
            };
          }
        ).then(() => {
          remaining--;

          if (remaining === 0) {
            resolve(results);
          }
        });
      });
    });
  };
}

Promise.myAllSettled([
  Promise.resolve("success"),
  Promise.reject("failure")
]).then(console.log);

Expected result

[
  { status: "fulfilled", value: "success" },
  { status: "rejected", reason: "failure" }
]

Explanation

Unlike Promise.all(), this method records rejections instead of rejecting the aggregate promise because an individual input rejects. The returned promise still rejects if the iterable itself cannot be consumed correctly.