What about expressions and motion math?

Scripting does not access individual properties of a layer, and thus it does not overlap with the functionality of expressions in After Effects, although it is based on a similar programmatical model. Scripting takes control of more global areas of After Effects, such as the application itself, the Project window, and the Render Queue, from which expressions can in some cases receive data but to which expressions cannot make changes.

The similarity between expressions and scripting is, however, apparent in that they are both drawn from the same language, ECMA standard JavaScript. Thus, knowing how to utilize one is helpful in understanding the other.

Motion math is no longer installed with After Effects 6.0; its funcionality has been superceded by expressions. Although scripting is not used to create animation data like expressions and motion math, all mathematical and logical operators common to ECMAScript are available in scripting.