3
Overview
Introduction to scripting in After Effects
A script is a series of commands that tells an application to perform a series of operations. You can use scripts
in most Adobe applications to automate repetitive tasks, perform complex calculations, and even use some
functionality not directly exposed through the graphical user interface. For example, you can direct After
Effects to reorder the layers in a composition, find and replace source text in text layers, or send an e-mail
message when rendering is complete.
See “Examples” on page 191 for examples of what scripts can do.
Although both the After Effects expressions language and the After Effects ExtendScript scripting language are
based on JavaScript, the expressions features and scripting features of After Effects are separate and distinct.
Expressions cannot access information from scripts (such as variables and functions). Whereas a script tells an
application to do something, an expression says that a property is something. However, because the After
Effects expression language and ExtendScript are both based on JavaScript, familiarity with either one is very
helpful in understanding the other.
The heart of a scriptable application is the object model. When you use Adobe After Effects, you create projects,
compositions, and render queue items along with all of the elements that they contain: footage, images, solids,
layers, masks, effects, and properties. Each of these items, in scripting terms, is an object. This guide describes
the ExtendScript objects that have been defined for After Effects projects.
The After Effects object model is composed of a project, items, compositions, layers, and render queue items.
Each object has its own special attributes, and every object in an After Effects project has its own identity
(although not all are accessible to scripting). You should be familiar with the After Effects object model in order
to create scripts.
NOTE: JavaScript objects normally referred to as “properties” are consistently called “attributes” in this guide, to
avoid confusion with After Effects’ own definition of a property (an animatable value of an effect, mask, or
transform within an individual layer).
Nearly all of what scripting can accomplish replicates what can be done by means of the After Effects graphical
user interface. A thorough knowledge of the application itself and its graphical user interface is essential to
understanding how to use scripting in After Effects.
The ExtendScript language
After Effects scripts use the Adobe ExtendScript language, which is an extended form of JavaScript used by
several Adobe applications, including Photoshop, Illustrator, and InDesign. ExtendScript implements the
JavaScript language according to the ECMA-262 specification. The After Effects scripting engine supports the
3rd Edition of the ECMA-262 Standard, including its notational and lexical conventions, types, objects, expres-
sions, and statements. ExtendScript also implements the E4X ECMA-357 specification, which defines access
to data in XML format.
ExtendScript defines a global debugging object, the dollar ($) object, and a reporting utility for ExtendScript
elements, the ExtendScript Reflection interface.