Asynchronous communication

✔️ async

• return : promise object

• async function f() {
    return Promise.resolve(value);
  }
  f.then(alert);

 

✔️ await

• suspends the function execution until the promise settles and then resumes it with the promise result (JavaScript engine can do other jobs in the meantime: execute other scripts, handle events, etc.)
• return : its result
• can’t use in regular functions

• async function f() {
    let promise = new Promise((resolve, reject) => {
      setTimeout(() => resolve("promise done"), 1000);
    });
    let result = await promise; // wait until the promise resolves
    alert(result); // "promise done" in 1 sec
  }

 

✔️ promise

• the eventual completion (or failure) of an asynchronous operation and its resulting value
• states : pending(initial state) / fulfilled / rejected

 

✔️ examples

• states : pending(initial state) / fulfilled / rejected

• let response = await fetch('/article/promise-chaining/user.json');
  let user = await response.json();
  console.log(user);

 

Ref) https://javascript.info/async-await / https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise