The intent of the Derivative JavaScript tab is to perform combined calculations. For example:

var temp = expensiveOperation();
var Result1 = temp*2;
var Result2 = fn(temp);

In this way, the expensiveCalculation only has to be done once.

you then write the Derivatives in the table as follows:

NewField1 : Integer = Result1
NewField2 : Integer = Result2

It is not intended for defining functions, though in JavaScript you can do that anywhere. There is no return from this JavaScript - the values are accessed directly, hence the JavaScript scope must be available to the table so it can "see" Result1 and Result2. The internal name of this JavaScript is "PreProcessor" - which gives you an idea of it's intent.

In the case of Filter, the JavaScript tab does expect a return value - a boolean determining whether to pass the record through or not. As only one result is required (unlike Derivative) we evaluate the script and expect a return. We don't need to make the scope of the JavaScript persist back to the filter table. In this case the JavaScript is working as a direct action, not a pre-processor.

-- ZhuBo - 24 Jan 2007