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Using the Expressions editor

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Use the different options in the expression editor to customize your expressions.

You can customize the code editor interface of the expression editor, including highlighting JavaScript syntax with custom colors, line numbers, code folding, and auto-complete. To customize these options, select Preferences > Scripting and Expressions.

Scripting and Expressions dialog
Scripting and Expressions dialog

Expression editor code interface

Customize syntax highlighting of JavaScript syntax and After Effects methods and properties:

Customize syntax highlighting
Customize syntax highlighting

  • You can assign custom colors to different types of syntax, the background, and text selection, as well as adjust the alpha ( opacity ) of the text selection. Click the dropper icon to select a color from the color wheel.
  • You can customize how the expression editor looks from the different themes available. Click the Theme drop-down list and select from the themes. You may also save custom themes.

Edit preferences: 

Edit preferences
Edit preferences

You can control how the expression snippets and the text editor look in the UI. Use these preferences to edit font size, syntax highlighting, adjust indents, and so on.

Code Preview box:

Code Preview box
Code Preview box

All changes to the syntax colors and other editor preferences can be previewed live in this code preview box.

Tip: Use throw to debug expressions inline. You can use this when you want to see the code error within the expression editor field, to save time and efficient debugging.

Throw to debug expressions inline
Throw to debug expressions inline

Example 1: Display error in your code snippet

  1. Open a comp in After Effects that has expression snippets.

  2. In the Timeline panel, select a layer and do Alt+Click. It displays the expression in the expression editor field.

    Expression Editor field
    Expression Editor field

  3. Click the editor field to enter the edit mode.

    Click in the editor to enable editing in the Expression Editor
    Click in the editor to enable editing in the Expression Editor

  4. In this example, select MILE in the first line, and change it to mile in lowercase. This triggers an error in the code, and After Effects displays an error message within the code snippet.

    Error message displayed in the code snippet
    Error message displayed in the code snippet

    After Effects also displays an error banner with details about the Line number where the error occurs.

    Error banner
    Error banner

Example 2: Auto-suggestions based on the commonly used components

  1. In the same expression, change the layer name from mile to MILE.

  2. As you type, After Effects displays a drop-down list with a set of suggestions that After Effects pulls from the layer names of the project.

    Layer name auto-suggestions
    Layer name auto-suggestions

Composition names, layer names, footage names, and effect names are all pulled into the autoComplete and shown in the correct context with their respective comp(), layer(), footage(), and effect() methods. This allows you to keep your expression active while referencing items in the project. You do not need to scroll the Timeline or open other panels to refer to properties or items using the pick whip.

More Expression resources

Now that you have understood some of the concepts behind expressions, come to the community for some real-life examples, and to share your work.

You can also check out Dan Ebberts' excellent collection of example expressions and tutorials on his MotionScript website.

The AE Enhancers forum also provides many examples and much information about expressions, as well as scripts and animation presets.

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