老師，請問一下 Promise.all 源码实现 2中，用index去判斷是不是等於promiseLength -1好像怪怪的，
因為forEach裡面每個promise都各自執行，有快有慢，有可能最後一個先去執行then，但是其他promise的then還沒執行。

    function processData (resolveSuccess: any, index: number) {
                allPromiseResolveSuccessValue[index] = resolveSuccess;
                if(index === promisesLength -1 ) {
                    resolve(allPromiseResolveSuccessValue);
                }
            }

不確定是不是應該改成allPromiseResolveSuccessValue.filter(Boolean).length=== promisesLength (filter(Boolean)是因為有可能會是sparse aray)

    function processData (resolveSuccess: any, index: number) {
                allPromiseResolveSuccessValue[index] = resolveSuccess;
                if(allPromiseResolveSuccessValue.filter(Boolean).length === promisesLength) {
                    resolve(allPromiseResolveSuccessValue);
                }
            }

感謝老師