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async_await.js
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async_await.js
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// An async function is declared using the 'async' keyword.
// It enables you to write asynchronous JavaScript in a cleaner way, avoiding "callback hell."
// Create an async function using the 'async' keyword.
async function getData() {
// Statements
}
// Async functions can take various arguments like normal functions but always return a promise.
// Example: Async function that returns a resolved promise with the value 1.
async function asyncFn() {
return 1;
}
// Equivalent function that returns a resolved promise with the value 1.
function fn() {
return Promise.resolve(1);
}
// You can handle the return value with .then() or .catch().
console.log(asyncFn()); // Promise {<fulfilled>: 1}
console.log(fn()); // Promise {<fulfilled>: 1}
asyncFn().then((v) => console.log(v)); // Logs 1
// Async functions can contain zero or more 'await' keywords that will wait for a promise to resolve or reject.
// Example: An async function with 'await' that waits for a promise to resolve after a delay.
async function asyncExample() {
const data = new Promise((resolve) =>
setTimeout(() => resolve('1'), 3000)
);
// 'await' pauses the function until the promise is resolved.
const result = await data;
console.log(result);
}
asyncExample(); // Logs '1' after a delay
console.log('sync'); // Logs 'sync'
// You can use try/catch/finally to handle async promises.
async function handle() {
try {
const data = await new Promise((resolve, reject) =>
setTimeout(() => resolve('4'), 4000)
);
console.log(data);
} catch (error) {
console.log(`Error: ${error}`);
} finally {
console.log('Finally block executed.');
}
}
handle(); // Logs '4' (after a delay), then 'Finally block executed.'