SyncTasks非 A + Promise 库

SyncTasks 是一个非 A + Promise 库，可以同步解析 promises。

这个是故意针对 ES6 promise 模式设计的，它在 JS 引擎的下一个时刻异步解析 promise 回调。 在许多情况下，异步解析是承诺的最安全和最容易理解的实现，但它给分辨率增加了很大的延迟，在大多数地方这是不必要的。 此外，当我们尝试使用标准ES6承诺包装IndexedDB体系结构时，它会崩溃，因为当控制权传递回主线程时，IndexedDB会关闭数据库连接。 我们开始构建NoSQLProvider并立即遇到了这个问题。 SyncTasks是解决该问题的方法，但也是异步编程问题的一种高效解决方案。 此外，我们已经使用了一个简单的可选取消机制，它也可以通过承诺解决方案进行链接（只要您通过SyncTasks承诺链接，并且不要混合使用非取消支持的承诺。）

示例代码：

function sendMeAStringLater(numberOfMilliseconds: number, theString: string): SyncTasks.Promise<string> {
    let defer = SyncTasks.Defer<string>();
    setTimeout(() => {
        defer.resolve(theString);
    }, numberOfMilliseconds);
    return defer.promise();
}

sendMeAStringLater(500, 'hi').then(myString => {
    console.log(myString);
});

// 500 ms after running this, you will end up with a new console log line, "hi".

添加消除：

function sendMeAStringLater(numberOfMilliseconds: number, theString: string): SyncTasks.Promise<string> {
    let defer = SyncTasks.Defer<string>();
    let didFinish = false;
    defer.onCancel(whyWasICancelled => {
        if (!didFinish) {
            didFinish = true;
            defer.reject(whyWasICancelled);
        }
    });
    setTimeout(() => {
        // Make sure to bail here if it's already done.  If you resolve a second time, it will throw an exception, since the
        // cancel already resolved it once.
        if (!didFinish) {
            didFinish = true;
            defer.resolve(theString);
        }
    }, numberOfMilliseconds);
    return defer.promise();
}

let promise = sendMeAStringLater(500, 'hi').then(myString => {
    console.log('Success: ' + myString);
}, errString => {
    console.log('Failure: ' + errString);
});

setTimeout(() => {
    promise.cancel('Sorry');
}, 200);

// 200 ms after running this, you will end up with a new console log line, "Failure: Sorry".  The success case will not be
// run because it was already resolved with failure.  If you change the 200ms timer to 600ms, then your console will change to
// "Success: hi" because the cancellation will happen after the success already did, so the `didFinish` check will swallow it.