我在lib/helper.js中编写了以下代码:
var myfunction = async function(x,y) {
....
return [variableA, variableB]
}
exports.myfunction = myfunction;
然后我尝试在另一个文件中使用它:
var helper = require('./helper.js');
var start = function(a,b){
....
const result = await helper.myfunction('test','test');
}
exports.start = start;
我得到一个错误:
await is only valid in async function
问题是什么?
当前回答
async / await的当前实现只支持async函数内部的await关键字。
var start = async function(a, b) {
}
对于那些感兴趣的人，顶层等待的提议目前处于阶段2:https://github.com/tc39/proposal-top-level-await
其他回答
async / await的当前实现只支持async函数内部的await关键字。
var start = async function(a, b) {
}
对于那些感兴趣的人，顶层等待的提议目前处于阶段2:https://github.com/tc39/proposal-top-level-await
错误不是指向myfunction，而是指向start。
async function start() {
....
const result = await helper.myfunction('test', 'test');
}
//函数 Const myfunction = async函数(x, y) { 返回( x, y, ]; ｝ //启动函数 Const start = async函数(a, b) { Const result = await myfunction('test'， 'test'); console.log(结果); ｝ //调用开始 开始();
我利用这个问题的机会来建议您使用await的一个已知的反模式，即:返回await。
错误的
async function myfunction() { console.log('Inside of myfunction'); } // Here we wait for the myfunction to finish // and then returns a promise that'll be waited for aswell // It's useless to wait the myfunction to finish before to return // we can simply returns a promise that will be resolved later // useless async here async function start() { // useless await here return await myfunction(); } // Call start (async() => { console.log('before start'); await start(); console.log('after start'); })();
正确的
async function myfunction() { console.log('Inside of myfunction'); } // Here we wait for the myfunction to finish // and then returns a promise that'll be waited for aswell // It's useless to wait the myfunction to finish before to return // we can simply returns a promise that will be resolved later // Also point that we don't use async keyword on the function because // we can simply returns the promise returned by myfunction function start() { return myfunction(); } // Call start (async() => { console.log('before start'); await start(); console.log('after start'); })();
另外，要知道有一种特殊情况，return await是正确且重要的:(使用try/catch)
“返回等待”是否存在性能问题?
在这篇不错的文章中找到下面的代码:使用Axios的Node中的HTTP请求
const axios = require('axios')
const getBreeds = async () => {
try {
return await axios.get('https://dog.ceo/api/breeds/list/all')
} catch (error) {
console.error(error)
}
}
const countBreeds = async () => {
const breeds = await getBreeds()
if (breeds.data.message) {
console.log(`Got ${Object.entries(breeds.data.message).length} breeds`)
}
}
countBreeds()
或者用Promise:
const axios = require('axios')
const getBreeds = () => {
try {
return axios.get('https://dog.ceo/api/breeds/list/all')
} catch (error) {
console.error(error)
}
}
const countBreeds = async () => {
const breeds = getBreeds()
.then(response => {
if (response.data.message) {
console.log(
`Got ${Object.entries(response.data.message).length} breeds`
)
}
})
.catch(error => {
console.log(error)
})
}
countBreeds()
如果在foreach中调用了async函数，则将其更新为for循环
如果你正在写一个Chrome扩展，你得到这个错误的代码在根，你可以修复它使用以下“变通”:
async function run() {
// Your async code here
const beers = await fetch("https://api.punkapi.com/v2/beers");
}
run();
基本上，你必须将异步代码包装在异步函数中，然后在不等待它的情况下调用该函数。
