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Many times it is required to execute a function many times after a certain period of time. For example, you may want to refresh your screen after a given time. Prototype provides a simple mechanism to implement it using PeriodicalExecuter object.
The advantage provided by PeriodicalExecuter is that it shields you against multiple parallel executions of the callback function.
The constructor takes two arguments:
Once launched, a PeriodicalExecuter triggers indefinitely, until the page unloads or the executer is stopped using stop() method.
Following is the example which will pop up a dialogue box after every 5 seconds untill you will stop it by pressing "cancel' button.
To understand it in better way you can Try it yourself.