async functions

async function showAvatar() { // read our JSON let response = await fetch('/article/promise-chaining/user.json'); let user = await response.json(); // read github user let githubResponse = await fetch(`https://api.github.com/users/${user.name}`); let githubUser = await githubResponse.json(); // show the avatar let img = document.createElement('img'); img.src = githubUser.avatar_url; img.className = "promise-avatar-example"; document.body.append(img); // wait 3 seconds await new Promise((resolve, reject) => setTimeout(resolve, 3000)); img.remove(); return githubUser; } showAvatar();

function resolveAfter2Seconds() { return new Promise(resolve => { setTimeout(() => { resolve('resolved'); }, 2000); }); } //async function: async function asyncCall() { console.log('calling'); const result = await resolveAfter2Seconds(); console.log(result); // expected output: 'resolved' } asyncCall();

js async await

/* Notes:
	1. written like synchronous code
    2. compatible with try/catch blocks
    3. avoids chaining .then statements
    4. async functions always return a promise
    5. function pauses on each await expression
    6. A non promise value is converted to 
       Promise.resolve(value) and then resolved
*/

// Syntax
// Function Declaration
async function myFunction(){
  await ... // some code goes here
}
  
// Arrow Declaration
const myFunction2 = async () => {
  await ... // some code goes here
}
  
 // OBJECT METHODS

const obj = {
	async getName() {
		return fetch('https://www.example.com');
	}
}

// IN A CLASS

class Obj {
	// getters and setter CANNOT be async
	async getResource {
		return fetch('https://www.example.com');
	}
}

Posted by: Guest on February-25-2020

async function f() { try { let response = await fetch('/no-user-here'); let user = await response.json(); } catch(err) { // catches errors both in fetch and response.json alert(err); } } f();

function resolveAfter2Seconds() { return new Promise(resolve => { setTimeout(() => { resolve('resolved'); }, 2000); }); } async function asyncCall() { console.log('calling'); const result = await resolveAfter2Seconds(); console.log(result); // expected output: 'resolved' } asyncCall();

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