使用 forloop 链接 Promise JS

Question

我正在尝试学习如何用 JS 链式承诺。我在这里看到了代码，他们使用 forloop JavaScript ES6 Promise for Loop 来完成它。我发现它很酷，并决定进行一些小的调整来尝试一下。但它没有奏效。如果您能告诉我为什么这不起作用，我将非常感激

这是我的代码：

//Goal: print from 0-10 in order at random times

function test() {

    for (let i = 0, p = Promise.resolve(); i < 10; i++) {

        p = p.then(createPromise(i));

    }

}

function createPromise(i) {

    return new Promise(resolve =>

        setTimeout(function () {

            console.log(i);

            resolve();

        }, Math.random() * 1000)

    )

}

test();

这是我的代码的输出

9

1

7

8

0

6

3

2

5

4

Answer 1

.then需要回调，而不是 Promise - 目前，您在循环内createPromise(i) 立即调用。创建一个在调用时返回Promise 的函数：p = p.then(() => createPromise(i));function test() {&nbsp; &nbsp; for (let i = 0, p = Promise.resolve(); i < 10; i++) {&nbsp; &nbsp; &nbsp; &nbsp; p = p.then(() => createPromise(i));&nbsp; &nbsp; }}function createPromise(i) {&nbsp; &nbsp; return new Promise(resolve =>&nbsp; &nbsp; &nbsp; &nbsp; setTimeout(function () {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; console.log(i);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; resolve();&nbsp; &nbsp; &nbsp; &nbsp; }, Math.random() * 1000)&nbsp; &nbsp; )}test();