为什么我的承诺会立即执行 [英] Why my promise executes immediately

问题描述

我想更深入地了解 Promise 如何在 JavaScript 中工作并尝试下一个代码:

I want to learn more thoroughly how promises work in JavaScript and trying the next code:

function delay(timeout) {
    return new Promise(function(resolve, reject){
        setTimeout(resolve,timeout);
    });
}

var promise = delay(10000);
promise.then(alert('after delay'));

我想为 JS setTimeout() 函数编写一个包装器，我假设在执行此代码时 10 秒后出现警报，但它立即显示，有人可以解释这里有什么问题吗?

I wanted to write a wrapper for JS setTimeout() function and I assume alert appearing after 10 sec while executing this code but it shows immediately, could someone explain what is wrong here?

推荐答案

promise.then(alert('after delay'));

给你:

1. 调用alert()
2. 将其返回值传递给then()

因此承诺不会立即解决.您只需在解决之前alert.

So the promise doesn't resolve immediately. You just alert before it resolves.

您必须将函数传递给then.

promise.then(alert.bind(window, 'after delay'));

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