How to use await in nodejs

In nodejs, await is used to pause execution in a non-blocking manner, waiting for a promise's asynchronous request, and waiting for the asynchronous method to complete execution; await can be used in async functions to wait for the return value of an async function; promise returns If the rejection is unsuccessful, the rejection value will be thrown and can be captured by "try/catch".

The operating environment of this article: Windows 10 system, nodejs version 12.19.0, Dell G3 computer.

How to use await in nodejs

Async/await usage was introduced in Node.js 7 night, but it is only possible to officially activate the async/await function in Node.js 8 and Javascript V8.

What is async/await? How to implement asynchronous operations using Promise in the past. The following case shows how to use Promise and Fetch API to fetch data:

function getTrace () { return fetch('https://www.jdon.com', { method: 'get' }) } getTrace() .then() .catch()

Using async/await, you can pause execution in a non-blocking manner and wait for the result to return. If the promise returns an unsuccessful rejection, the rejection value will be thrown and can be captured by try/catch. The above case can be written as follows using async/await:

function async getTrace () { let pageContenttry { pageContent = await fetch('https://www.jdon.com', { method: 'get' }) } catch (ex) { console.error(ex) } return pageContent} getTrace() .then()

Let’s look at the case of using async/await in Node.js, using setimeout to delay the execution of a function, and using async/await encapsulation:

// app.jsconst timeout = function (delay) { return new Promise((resolve, reject) => { setTimeout(() => { resolve() }, delay) }) } async function timer () { console.log ('timer started') await Promise.resolve(timeout(100)); console.log('timer finished') } timer()

Create the app.js file and run:

node app.js

If it cannot run, it may be that nodejs is a nightly version and does not officially support async/await. The command line should be:

node --harmony-async-await app.js

Recommended learning: "nodejs video tutorial"

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