setImmediate method
Syntax
var retVal = window.setImmediate(handler, arguments);Standards information
Parameters
- handler [in]
-
Type: any
The function to be called.
- arguments [in, optional]
-
Type: any
Arguments to be passed to the function.
Return value
Type: IntegerA handle to the request.
Remarks
JavaScript operations run in the same thread as events, display updates, and other additional tasks. As a result, extended JavaScript operations (such as functions containing many lines of code) prevent additional tasks from being handled. In turn, this makes an application appear to be unresponsive because events (such as onclick or onkeypress) are not handled and the screen is not updated until the extended operation completes.
The setImmediate method schedules the function specified in the handler parameterto run after the current script block completes.If additional actions are pending when the current script block completes, they are processed before the handler function is called. This effectively creates a yield between the current script block and the handler function.
If you break extended operations into separate functions, you can use setImmediate to call each function in sequence. When you do this, setImmediate allows additional tasks to complete before calling each function in the sequence. In turn, this enables the application to respond to user input and to handle additional tasks in a predictable and responsive fashion.
For more information, see the setImmediate TestDrive demo.
Note
Some developers use setTimeout (or setInterval) to create events that accomplish similar results; however, there are subtle, but important differences between the two techniques.
The setTimeout method is restricted to 250
requests per second on most systems. This means that setTimeout(0, handler)
waits roughly 4ms before executing, even if no additional actions are pending. In contrast, setImmediate yields between each request, no matter how many requests are waiting
to processed. If no additional actions are pending, setImmediate calls the handler function immediately.