Promise.all(), allSettled(), race(), any()

Syntax

Promise.all([p1, p2, p3])
Promise.allSettled([p1, p2, p3])

Examples

const userPromise = fetch("/api/user").then(r => r.json());
const postsPromise = fetch("/api/posts").then(r => r.json());

Promise.all([userPromise, postsPromise])
  .then(([user, posts]) => {
    console.log(user, posts);
  })
  .catch(error => {
    console.log("At least one request failed:", error.message);
  });

const promises = [
  Promise.resolve("Success 1"),
  Promise.reject("Failure 1"),
  Promise.resolve("Success 2")
];

Promise.allSettled(promises).then(results => {
  results.forEach(result => {
    if (result.status === "fulfilled") {
      console.log("Success:", result.value);
    } else {
      console.log("Failed:", result.reason);
    }
  });
});

Best practices

• Use Promise.all() when every operation must succeed for the result to be useful - like loading required page data
• Use Promise.allSettled() when partial success is acceptable and you want to know exactly what failed without stopping the rest
• Use Promise.race() for timeout patterns - race a real request against a promise that rejects after a delay
• Avoid awaiting promises sequentially in a loop when they are independent - use Promise.all() with map() to run them in parallel instead

At a glance

Purpose

Application logic and interaction

File extension

.js · .mjs

Runs in

Browsers and JavaScript runtimes

Usually used with

HTML, CSS and Web APIs

Specifications & further reading

• ECMAScript specification

Related JavaScript documentation