How to Use the async and await Keywords

Kunal NalawadeAbout 2 min

How to Use the async and await Keywords 관련

The JavaScript Interview Prep Handbook – Essential Topics to Know + Code Examples

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The JavaScript Interview Prep Handbook – Essential Topics to Know + Code Examples

await keyword pauses execution of a function till a promise has been resolved or rejected. await can only be used inside an async function. Let's take an example:

function dataPromise() {
    return new Promise(resolve => {
        setTimeout(() => resolve("Data retrieved"), 500);
    });
}

async function fetchData() {
    try {
        const res = await dataPromise();
        console.log(res); // Data retrieved (after 500ms)
    } catch(err) {
        console.log(err);
    }
}

fetchData();

When dataPromise() is called, the execution of the function pauses for 500ms. The execution continues after the promise has resolved. To handle errors, surround the code with a try-catch block.

The await keyword also makes it easier to work with multiple promises that run one after the other.

function promise1() {
    return new Promise(resolve => {
        setTimeout(() => resolve("Promise 1 resolved"), 500);
    });
}

function promise2() {
    return new Promise(resolve => {
        setTimeout(() => resolve("Promise 2 resolved"), 300);
    });
}

async function fetchData() {
    try {
        const res1 = await promise1();
        console.log(res1); // Promise 1 resolved (after 500ms)
        const res2 = await promise2();
        console.log(res2); // Promise 2 resolved (after 300ms)
    } catch(err) {
        console.log(err);
    }
}

fetchData();

async and await makes it easier to work with promises and also makes your code cleaner and readable by removing nesting in the code.