Prototype PeriodicalExecuter對象學習

2019-11-21 01:15:37

字體：大中小

供稿：網(wǎng)友

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.

這個對象就是可以周期性的執(zhí)行某個方法，但是在它內(nèi)部維持了一個狀態(tài)，可以防止由于某些原因一次調(diào)用沒執(zhí)行，然后下一次調(diào)用又來了，這樣會造成連續(xù)執(zhí)行兩次方法。上面的第二斷英文就是這個意思。

幫助文檔上說這個對象只提供了一個方法stop，但是在我看的源碼里還提供了一個事件onTimerEvent，應該可以在某個時候觸發(fā)這個事件。但幫助文檔上沒有給出示例。

這個對象源碼比較簡單，這里直接貼出來了，就不再注釋了：

復制代碼代碼如下:

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：

復制代碼代碼如下:

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... 

上一篇：Prototype Array對象學習

下一篇：Prototype String對象學習