为什么我的 Promises 数组在调用 Promise.all() 之前运行? [英] Why is my array of Promises running before calling Promise.all()?

问题描述

我正在尝试创建一个 Promise 数组，然后使用 Promise.all() 解决它们.我正在使用 got，它返回一个承诺.

I am trying to create an array of Promises, then resolve them with Promise.all(). I am using got, which returns a promise.

我的代码有效，但我不完全理解如何.这是:

My code works, but I don't fully understand how. Here it is:

const got = require('got');

const url = 'myUrl';
const params = ['param1', 'param2', 'param3'];

let promiseArray = [];
for (param of params) {
    promiseArray.push(got(url + param));
}

// Inspect the promises
for (promise of promiseArray) {
    console.log(JSON.stringify(promise));
    // Output: promise: {"_pending":true,"_canceled":false,"_promise":{}}
}

Promise.all(promiseArray).then((results) => {
     // Operate on results - works just fine
}).catch((e) => {
    // Error handling logic
});

让我失望的是，当我将 Promise 添加到数组中时，它们被标记为pending"，这意味着它们已经开始.

What throws me off is that the Promises are marked as "pending" when I add them into the array, which means they have already started.

我认为它们应该在 promiseArray 中处于非活动状态，并且 Promise.all(promiseArray) 会启动它们并解决它们.

I would think that they should lie inactive in promiseArray, and Promise.all(promiseArray) would both start them and resolve them.

这是否意味着我要启动它们两次?

Does this mean I am starting them twice?

推荐答案

您不会启动它们两次.Promise 一创建就开始运行——或者只要 JS 引擎找到足够的资源来启动它们.您无法控制它们何时真正开始.

You're not starting them twice. Promises start running as soon as they're created - or as soon as the JS engine finds enough resources to start them. You have no control on when they actually start.

所有 Promise.all() 所做的就是等待它们全部解决(解决或拒绝).Promise.all() 不会干扰或影响 Promise 本身的执行顺序/时间.

All Promise.all() does is wait for all of them to settle (resolve or reject). Promise.all() does not interfere with nor influence the order/timing of execution of the promise itself.

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