what is the use of async and await in javascript 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: how to make an async function
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();
Example 3: javascript async script
<script async src="script.js"></script>
Example 4: async await javascript
function hello() {
return new Promise((resolve,reject) => {
setTimeout(() => {
resolve('I am adam.');
}, 2000);
});
}
async function async_msg() {
try {
let msg = await hello();
console.log(msg);
}
catch(e) {
console.log('Error!', e);
}
}
async_msg(); //output - I am adam.
Example 5: 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 6: 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();