The After Effects expression language is based on JavaScript 1.2, with an extended set of built-in objects. After Effects uses only the core standard JavaScript 1.2 language, not the web browser–specific extensions. After Effects contains its own set of extension objects—such as Layer, Comp, Footage, and Camera—that you can use to access most of the values in an After Effects project.

For more information about JavaScript, see a JavaScript reference manual.

When creating expressions, keep the following in mind:

• JavaScript is case-sensitive.

• Semicolons are required to separate statements or lines.

• Spaces between words are ignored, except within a string.

In JavaScript, a value stored in an object is called a property. However, After Effects uses the term property to refer to layer attributes as defined in the Timeline panel. Consequently, for clarity, After Effects documentation refers to a JavaScript property as a method when the property takes arguments, or an attribute when it does not.

The value of an expression is the value of the last statement evaluated.