There are two ways to invoke a remote object through Remote Scripting: synchronously and asynchronously. The asynchronous approach is particularly useful because it doesn’t stop the user from working within the page while an operation is in progress.
An asynchronous mechanism needs a callback function to let the page know about the success or failure of the operation. A callback function is a script function with a prototype like this:
Here “co” is an argument that evaluates to a Call Object the return value of any RS operation. The callback executes on the client, while the RS proxy is responsible for calling it when appropriate. In programming, a callback function always has a fixed prototype and can accept arguments that refer to items to work on. This reference is called the context where the callback will work.
The RSExecute function is the principal means for issuing RS calls. It lets you run synchronous as well as asynchronous calls. If you specify a callback function, then the call is asynchronous; otherwise, it’s synchronous.