promise async await code example
Example 1: async await
const data = async () => {
const got = await fetch('https://jsonplaceholder.typicode.com/todos/1');
console.log(await got.json())
}
data();
Example 2: async await
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();
Example 3: nodejs promise async
// server.js
function square(x) {
return new Promise(resolve => {
setTimeout(() => {
resolve(Math.pow(x, 2));
}, 2000);
});
}
async function layer(x)
{
const value = await square(x);
console.log(value);
}
layer(10);
Example 4: 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');
}
}
Example 5: async await
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();
Example 6: async await
async function showAvatar() {
// read
await setTimeout(resolve, 3000);
// read next 3s
}
showAvatar();