What's the difference between Async Await and Promise in JavaScript All In One
AsyncvsPromise
demos
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Promise
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise
Async
The async function declaration creates a binding of a new async function to a given name.
The await keyword is permitted within the function body, enabling asynchronous, promise-based behavior to be written in a cleaner style and avoiding the need to explicitly configure promise chains.
简化 Promise 链式调用的显式配置，写法更优雅
function resolveAfter2Seconds() {
return new Promise((resolve) => {
console.log('wait1...');
setTimeout(() => {
console.log('wait3...', typeof resolve);
resolve('resolved');
console.log('wait4...');
}, 2000);
console.log('wait2...');
});
}
// async function declaration ✅
async function asyncCall() {
console.log('calling 0 ');
const result = await resolveAfter2Seconds();
console.log(`result 5`, result);
}
asyncCall();
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function
The async function keywords can be used to define an async function inside an expression.
// async function expression
function resolveAfter2Seconds(x) {
return new Promise((resolve) => {
setTimeout(() => {
resolve(x);
}, 2000);
});
}
// async function expression assigned to a variable
const add = async function (x) {
const a = await resolveAfter2Seconds(20);
const b = await resolveAfter2Seconds(30);
return x + a + b;
};
add(10).then((v) => {
console.log(v); // prints 60 after 4 seconds.
});
// async function expression used as an IIFE
(async function (x) {
const p1 = resolveAfter2Seconds(20);
const p2 = resolveAfter2Seconds(30);
return x + (await p1) + (await p2);
})(10).then((v) => {
console.log(v); // prints 60 after 2 seconds.
});
// async function `name`
async function name(param0) {
statements
}
async function name(param0, param1) {
statements
}
async function name(param0, param1, /* …, */ paramN) {
statements
}
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/async_function
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function*
Await
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/await
refs
https://javascript.info/async-await
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