Yet another Promise case

[2zH]

const sleep = t => () => new Promise(resolve => setTimeout(() => {console.log(t); resolve(t)}, t))
const example = [sleep(3000), sleep(1000), sleep(5000)]
const promiseReducer = example.reduce.bind(example)

// Test case 1
promiseReducer((r, f) => r.then(() => f()), Promise.resolve())
// 3000
// 1000
// 5000

// Test case 2
promiseReducer(async (r, f) => await f(), Promise.resolve())
// 1000
// 3000
// 5000

// Test case 3
promiseReducer(async (r, f) => { let result = await f; return result }, Promise.resolve())
// 1000
// 3000
// 5000

// Test case 4
promiseReducer(async (r, f) => { let a = await f();await sleep(2000)();console.log(a);return a; }, Promise.resolve())
// 1000
// 3000
// 2000
// 1000
// 5000
// 2000
// 3000
// 2000
// 5000

// Test case 5
promiseReducer(async (r, f) => { await r;let a = await f();await sleep(2000)();console.log(a);return a; }, Promise.resolve())
// 3000
// 2000
// 3000
// 1000
// 2000
// 1000
// 5000
// 2000
// 5000

[2zH]

Promise.all :: [Promise] -> Promise Promise.all 的执行过程保持异步。