create-expression-lib 🐱‍👤

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A CLI for creating Expression Libraries for After Effects, in TypeScript.

npx create-expression-lib

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Why?

At Motion Developer we maintain a lot of expression (.jsx) libraries, such as eKeys, eBox, and aeFunctions. This allows us to:

• Share code between expressions and projects
• Edit code in powerful editor (such as VS Code)
• Improve performance
• Build abstractions for complex tasks

For more info on writing expressions in .jsx files, see our article: How to write expressions in external jsx files

create-expression-lib is a CLI to create After Effects expression libraries, that enables you to:

• Write in TypeScript (.ts files)
• Split expressions into multiple files, to be bundled at build time
• Write syntactically correct JavaScript, allowing:
  • Testing
  • Linting
  • Automatic formatting

Requirements

To use this template you need to have Node installed on your system.

For the best experience, it's recommended you also install and use:

• Git
• VS Code
• GitHub CLI

Creating the library

npx create-expression-lib project-name
cd project-name

Arguments:

• --install: install npm packages (-i)
• --git: initialize with git repo (-g)
• --yes: skip prompts (-y)

This sets up all the files necessary in a 'project-name' folder to create expression libraries in TypeScript.

Edit your library

If you didn't install the packages when creating the library with --install make sure to run npm install.

1. Start Rollup

   Start Rollup in watch mode to automatically refresh your code as you make changes, by running:

   npm run watch

   You can run also run a once off build: npm run build

2. Edit the src files

   The index.ts contains an example expression setup.

   Any values exported from this file will be included in your library, for example:

   export { someValue };

3. Import the dist file into After Effects

   Use the compiled output file as you would any other .jsx library. Any changes to the src files will be live updated, and After Effects will update the result of your expression.

4. Distribute releases

   To distribute your output file using Github releases (via Hub), use the command:

   npm run release

   This will use the GitHub CLI to create a new tag and release

   The release version number is the "version" in package.json, and it will attach the "main" file to the release.

   You can add this version to the output file by placing the string _npmVersion in your code, which will be replaced with the version number in package.json at build time.

After Effects API

This template uses the expression-globals-typescript package to provide types for the expressions API.

Classes

To create layers, compositions and properties, you can use the classes exported from the library. For example:

import { Comp, Layer } from "expression-globals-typescript";
const thisComp = new Comp();
const thisLayer = new Layer();

To create properties (such as position or scale), you can use the Property class.

import { Property, Vector } from "expression-globals-typescript";
const thisProperty = new Property<Vector>([0, 100]);

The Property constructor takes a value to set as the property value, and a type (<>) to set as the type for the property.

After Effects Types

You can import After Effect's specific types such as Color and Vector from the package to properly type your expressions.

To see all the Types and Base Objects available, see the expression-globals-typescript source code.

Testing

You can test your expression library code using Jest, which comes pre-configured in this template repo.

You write tests in the index.test.ts file, importing the code you want to test from index.ts, for example:

import { welcome } from "./index";

test("returns correct welcome string", () => {
  expect(welcome("test")).toEqual("Welcome test!");
});

And then run the test suite:

npm run test

Which will run Jest in watch mode.

You can learn more about testing using Jest from the Jest docs.

Configuration

There a couple of files you may wish to change to reflect the content of your project:

• package.json:
  • version: The current version of the library, which is used for releases and added to dist files.
  • main: The build output file which will be attached to releases
• rollup.config.js:
  • input: The source file to be built
  • typescript(): Custom typescript compiler options

How

• expression-globals-typescript mocks the After Effects expressions API in typescript, so you can use global functions and objects such as linear() and time, while also providing expression specific types such as Layer.

• Rollup is a lightweight module bundler that handles outputting the .jsx file via the plugins below.

• The Rollup Typescript plugin runs the TypeScript compiler

• The Rollup plugin rollup-plugin-ae-jsx transforms the JavaScript output into After Effects JSON (.jsx) compliant syntax

• Testing via Jest, and ts-jest