使用Promise等待轮询条件满足 [英] Use Promise to wait until polled condition is satisfied

问题描述

我需要创建一个JavaScript Promise，在特定条件为真之前无法解析。假设我有一个第三方库，我需要等到该库中存在某个数据条件。

I need to create a JavaScript Promise that will not resolve until a specific condition is true. Let's say I have a 3rd party library, and I need to wait until a certain data condition exists within that library.

我感兴趣的场景是那里有一个除了简单的轮询之外，没办法知道什么时候满足这个条件。

The scenario I am interested in is one where there is no way to know when this condition is satisfied other than by simply polling.

我可以创建一个等待它的承诺 - 这个代码有效，但是有更好的或者更简洁的方法解决这个问题？

I can create a promise that waits on it - and this code works, but is there a better or more concise approach to this problem?

function ensureFooIsSet() {
    return new Promise(function (resolve, reject) {
        waitForFoo(resolve);
    });
}

function waitForFoo(resolve) {
    if (!lib.foo) {
        setTimeout(waitForFoo.bind(this, resolve), 30);
    } else {
        resolve();
    }
}

用法：

ensureFooIsSet().then(function(){
    ...
});

我通常会实现最大轮询时间，但不希望这样在此处解决问题。

I would normally implement a max poll time, but didn't want that to cloud the issue here.

推荐答案

一个小变化是使用命名的IIFE，以便您的代码更简洁一点，避免污染外部范围：

A small variation would be to use a named IIFE so that your code is a little more concise and avoids polluting the external scope:

function ensureFooIsSet() {
    return new Promise(function (resolve, reject) {
        (function waitForFoo(){
            if (lib.foo) return resolve();
            setTimeout(waitForFoo, 30);
        })();
    });
}

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