何时调用Promise.then（）挂钩？ [英] When Promise.then() hooks are called?

问题描述

我发现Firefox的承诺中推迟了完整性通知。断言失败，因为onFullfilled（）被称为为时太晚 ^* 。

I observe deferring of completeness notifications in Firefox's promises. Following assertion fails, because onFullfilled() is called too late^*.

var resolved = false;
function onFullfilled() {
    resolved = true;
    log("Completed");
}
Promise.resolve(true).then(onFullfilled);
assert(resolved, "Promise completed promise should call resolution hook immediately.");

何时保证在Promise分辨率上精确调用onFullfilled（）？

When exactly onFullfilled() is guaranteed to be called on Promise resolution?

_{*在我的情况下，测试框架报告声明失败后出现 Completed日志消息。}

推荐答案

在所有同步代码执行完毕后，始终称为Prom决议挂钩。

Promise resolution hooks are always called after all sync code is executed. This is by design - and is done in order to prevent race conditions.

由于promise有时异步地解析它们的规范要求，所以总是 被异步地解决。因此执行相同的代码路径。承诺守卫您反对Zalgo 。

Since promises sometimes resolve asynchronously the specification mandates they are always resolved asynchronously so the same code path executes. Promises guard you against Zalgo.

它是在此处指定：

onFulfilled或onRejected必须在执行上下文堆栈仅包含平台代码之前被调用。

onFulfilled or onRejected must not be called until the execution context stack contains only platform code.

很多测试框架-即Mocha支持通过返回承诺直接使用承诺语法测试承诺。

A lot of test frameworks - namely Mocha support testing promises directly with promise-syntax - by returning a promise.

it("does something", function(){
    return aPromise; // if aPromise resolves the test passes
})

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