Defining +the callback handler for an asynchronous method

The callback handler method is used with an asynchronous method call +to retrieve the information requested by the call. The asynchronous call initiates +the callback handler and then returns a TransactionID. +This ID is used to map the asynchronous call to the correct callback handler +instance and the result information it returns. You can call the result handler +method from within the callback handler.

Define a callback handler method for any Service +API method that is called asynchronously. Use the following method +signature:

+ + + +

callback(transId, eventCode, result)

The system supplies the expected arguments:

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**Table:** Callback arguments
+ Argument +	+ Description +	+ Value +
+ `transId` +	+ This is a number representing the transaction that called the callback +handler. + `TransactionID` was returned as part of the result +of the initial asynchronous call. +
+ `eventCode` +	+ This is a number representing the callback return status. +	+ Value - Description: + `2` - Event completed + `4` - Event error + `9` - Event in progress +
+ `result` +	+ This is an object for holding the callback return value. +	+ See the following table. +

The callback handler returns an object that contains the requested information, +an error code, and an error message:

+ + + + + + + + + + + + + + + + + + + + + +

**Table:** Callback return +value
+ Property +	+ Description +	+ Value +
+ `[result.ReturnValue]` +	+ This contains the information requested by the asynchronous call that +initiated the callback handler. + If an asynchronous call does not request any information to be returned, +this property is not included in the callback return value. In this case, +the callback handler only returns `ErrorCode` and `ErrorMessage`. +	+ Depends on the Service +API and the asynchronous method that was called. Not all calls return +this property. See the appropriate method definition. +
+ `result.ErrorCode` +	+ This is a number that specifies a predefined error code. +	+ See Service API error codes. +
+ `result.ErrorMessage` +	+ This is a text string that describes the error. +	+ Depends on the Service +API and the asynchronous method that was called. See the appropriate +method definition. +

+ + + +