如何检查Promise是否有待处理 [英] How to check if a Promise is pending

问题描述

我有这种情况，我想知道承诺的状态。下面，函数 start 只调用 someTest ，如果它不再运行（Promise未挂起）。可以多次调用 start 函数，但如果在测试仍在运行时调用它，它将不会等待并返回 false

I have this situation in which I would like to know what the status is of a promise. Below, the function start only calls someTest if it is not running anymore (Promise is not pending). The start function can be called many times, but if its called while the tests are still running, its not going to wait and returns just false

class RunTest {
    start() {
         retVal = false;

         if (!this.promise) {
             this.promise = this.someTest();
             retVal = true;                
         }

         if ( /* if promise is resolved/rejected or not pending */ ) {
             this.promise = this.someTest();
             retVal = true;
         }

         return retVal;
    }

    someTest() {
        return new Promise((resolve, reject) => {
            // some tests go inhere
        });
    }
}

我找不到简单检查状态的方法一个承诺。像 this.promise.isPending 之类的东西会很好:)任何帮助都会受到赞赏！

I cannot find a way to simply check the status of a promise. Something like this.promise.isPending would be nice :) Any help would be appreciated!

推荐答案

您可以附加一个然后处理程序，在promise（或<）上设置 done 标志code> RunTest 实例（如果您愿意），并测试：

You can attach a then handler that sets a done flag on the promise (or the RunTest instance if you prefer), and test that:

     if (!this.promise) {
         this.promise = this.someTest();
         this.promise.catch(() => {}).then(() => { this.promise.done = true; });
         retVal = true;                
     }

     if ( this.promise.done ) {
         this.promise = this.someTest();
         this.promise.catch(() => {}).then(() => { this.promise.done = true; });
         retVal = true;
     }

注意空 catch（） handler，无论promise的结果如何，都要调用处理程序是至关重要的。
您可能希望将其包装在函数中以保持代码DRY。

Notice the empty catch() handler, it's crucial in order to have the handler called regardless of the outcome of the promise. You probably want to wrap that in a function though to keep the code DRY.

这篇关于如何检查Promise是否有待处理的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！