Prototype 学习——PeriodicalExecuter对象

This is a simple facility for periodical execution of a function. This essentially encapsulates the native clearInterval/setInterval mechanism found in native Window objects.

This is especially useful if you use one to interact with the user at given intervals (e.g. use a prompt or confirm call): this will avoid multiple message boxes all waiting to be actioned.

这个对象就是可以周期性的执行某个方法，但是在它内部维持了一个状态，可以防止由于某些原因一次调用没执行，然后下一次调用又来了，这样会造成连续执行两次方法。上面的第二断英文就是这个意思。

帮助文档上说这个对象只提供了一个方法stop，但是在我看的源码里还提供了一个事件onTimerEvent，应该可以在某个时候触发这个事件。但帮助文档上没有给出示例。

这个对象源码比较简单，这里直接贴出来了，就不再注释了：

var PeriodicalExecuter = Class.create({ initialize: function(callback, frequency) { this.callback = callback; this.frequency = frequency; this.currentlyExecuting = false; this.registerCallback(); }, registerCallback: function() { this.timer = setInterval(this.onTimerEvent.bind(this), this.frequency * 1000); }, execute: function() { this.callback(this); }, stop: function() { if (!this.timer) return; clearInterval(this.timer); this.timer = null; }, onTimerEvent: function() { if (!this.currentlyExecuting) { try { this.currentlyExecuting = true; this.execute(); } catch(e) { /* empty catch for clients that don't support try/finally */ } finally { this.currentlyExecuting = false; } } }});

 

看一下示例：

new PeriodicalExecuter(function(pe) { if (!confirm('Want me to annoy you again later?')) pe.stop(); }, 5); // Note that there won't be a stack of such messages if the user takes too long // answering to the question...