• 异步方法补丁

    异步方法补丁

    这里我们将看看如何通过异步回调传播zone的基本机制。 （注意：实际工作情况有点复杂，因为它们通过稍后讨论的任务调度机制进行调度，为了清楚起见，该示例进行了简化）。

    1. // 保存原始的setTimeout引用
    2. let originalSetTimeout = window.setTimeout;
    3. // Overwrite the API with a function which wraps callback in zone.
    4. window.setTimeout = function(callback, delay) {
    5.   // Invoke the original API but wrap the callback in zone.
    6.   return originalSetTimeout(
    7.     // Wrap the callback method
    8.     Zone.current.wrap(callback),
    9.     delay
    10.   );
    11. }
    12. // Return a wrapped version of the callback which restores zone.
    13. Zone.prototype.wrap[c] = function(callback) {
    14.   // Capture the current zone
    15.   let capturedZone = this;
    16.   // Return a closure which executes the original closure in zone.
    17.   return function() {
    18.     // Invoke the original callback in the captured zone.
    19.     return capturedZone.runGuarded(callback, this, arguments);
    20.   };
    21. };

    关键点：

    • Zones 的猴子补丁方法只修补一次。
    • 进入/离开 zone 只需更改Zone.current的值。（不需要进一步的猴子补丁）
    • Zone.prototype.wrap method provides convenience for wrapping callbacks. (The wrapped callback is executed through Zone.prototype.runGuarded())
    • Zone.prototype.runGuarded() is just like Zone.prototype.run(), but with extra try-catch block for handling exceptions described later.
    1. // Save the original reference to Promise.prototype.then.
    2. let originalPromiseThen = Promise.prototype.then;
    3. // Overwrite the API with function which wraps the arguments
    4. // NOTE: this is simplified as actual API has more arguments.
    5. Promise.prototype.then = function(callback) {
    6.   // Capture the current zone
    7.   let capturedZone = Zone.current;
    8.   // Return a closure which executes the original closure in zone.
    9.   function wrappedCallback() {
    10.     return capturedZone.run(callback, this, arguments);
    11.   };
    12.   // Invoke the original callback in the captured zone.
    13.   return originalPromiseThen.call(this, [wrappedCallback]);
    14. };

    关键点：

    • Promises handle their own exceptions and so they can’t use Zone.prototype.wrap(). (We could have separate API, but Promise is the exception to the rule, and so I did not feel justified creating its own API.)
    • Promise API较多，在此示例中未显式显示。