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 of an async function Value; promise returns an unsuccessful rejection, and 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 capture 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 pageContent
try { 
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.js
const 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 this 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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