使用async / await动态生成promise链

Question

Say, I need to repeat an AJAX request N times sequentially.

Normally (ie without async/await), I would use reduce to chain promises:

 function timeout (ms = 1000) { return new Promise(resolve => setTimeout(resolve, ms)) } function request (message, ms = 1000) { return timeout(ms).then(() => console.log(message)) } function makeArray (i) { return new Array(i).fill(null); } makeArray(5).reduce( (promise, _, i) => promise.then(() => request(i)), Promise.resolve() ) 

How do I rewrite this code with async/await?

Instead of promise.then(() => request(i)) I want to do await request(i) .

All my attempts ended up running promises in parallel. I want sequentially.

Answer 1

Remember await can only be invoked from a an async function.

Here I've just wrapped inside a function run , it could even be an IIFE..

In most cases when you start using async / await , you'll be calling from another async function anyway, so this little run stub wouldn't be required.

 function timeout (ms = 1000) { return new Promise(resolve => setTimeout(resolve, ms)) } function request (message, ms = 1000) { return timeout(ms).then(() => console.log(message)) } async function run() { for (let trys = 0; trys < 5; trys ++) { await request(trys); } } run();