Lit and Figma

In this article I will go over how to set up a Lit web component and use it to create a figma plugin.

TLDR You can find the final source here.

Prerequisites 

Getting Started 

We can start off by creating a empty directory and naming it with snake_case whatever we want.

mkdir figma_lit_example
cd figma_lit_example

Web Setup 

Now we are in the figma_lit_example directory and can setup Figma and Lit. Let's start with node.

npm init -y

This will setup the basics for a node project and install the packages we need. Now lets add some config files. Now open the package.json and replace it with the following:

{
  "name": "figma_lit_example",
  "version": "1.0.0",
  "description": "Lit Figma Plugin",
  "dependencies": {
    "lit": "^2.0.0-rc.1"
  },
  "devDependencies": {
    "@figma/plugin-typings": "^1.23.0",
    "html-webpack-inline-source-plugin": "^1.0.0-beta.2",
    "html-webpack-plugin": "^4.3.0",
    "css-loader": "^5.2.4",
    "ts-loader": "^8.0.0",
    "typescript": "^4.2.4",
    "url-loader": "^4.1.1",
    "webpack": "^4.44.1",
    "webpack-cli": "^4.6.0"
  },
  "scripts": {
    "dev": "npx webpack --mode=development --watch",
    "copy": "mkdir -p lit-plugin && cp ./manifest.json ./lit-plugin/manifest.json && cp ./dist/ui.html ./lit-plugin/ui.html && cp ./dist/code.js ./lit-plugin/code.js",
    "build": "npx webpack --mode=production && npm run copy",
    "zip": "npm run build && zip -r lit-plugin.zip lit-plugin"
  },
  "browserslist": [
    "last 1 Chrome versions"
  ],
  "keywords": [],
  "author": "",
  "license": "ISC"
}

This will add everything we need and add the scripts we need for development and production. Then run the following:

npm i

This will install everything we need to get started. Now we need to setup some config files.

touch tsconfig.json
touch webpack.config.ts

This will create 2 files. Now open up tsconfig.json and paste the following:

{
  "compilerOptions": {
    "target": "es2017",
    "module": "esNext",
    "moduleResolution": "node",
    "lib": ["es2017", "dom", "dom.iterable"],
    "typeRoots": ["./node_modules/@types", "./node_modules/@figma"],
    "declaration": true,
    "sourceMap": true,
    "inlineSources": true,
    "noUnusedLocals": true,
    "noImplicitReturns": true,
    "noFallthroughCasesInSwitch": true,
    "experimentalDecorators": true,
    "skipLibCheck": true,
    "strict": true,
    "noImplicitAny": false,
    "outDir": "./lib",
    "baseUrl": "./packages",
    "importHelpers": true,
    "plugins": [
      {
        "name": "ts-lit-plugin",
        "rules": {
          "no-unknown-tag-name": "error",
          "no-unclosed-tag": "error",
          "no-unknown-property": "error",
          "no-unintended-mixed-binding": "error",
          "no-invalid-boolean-binding": "error",
          "no-expressionless-property-binding": "error",
          "no-noncallable-event-binding": "error",
          "no-boolean-in-attribute-binding": "error",
          "no-complex-attribute-binding": "error",
          "no-nullable-attribute-binding": "error",
          "no-incompatible-type-binding": "error",
          "no-invalid-directive-binding": "error",
          "no-incompatible-property-type": "error",
          "no-unknown-property-converter": "error",
          "no-invalid-attribute-name": "error",
          "no-invalid-tag-name": "error",
          "no-unknown-attribute": "off",
          "no-unknown-event": "off",
          "no-unknown-slot": "off",
          "no-invalid-css": "off"
        }
      }
    ]
  },
  "include": ["src/**/*.ts"],
  "references": []
}

This is a basic typescript config. Now open up webpack.config.ts and paste the following:

const HtmlWebpackInlineSourcePlugin = require("html-webpack-inline-source-plugin");
const HtmlWebpackPlugin = require("html-webpack-plugin");
const path = require("path");

module.exports = (env, argv) => ({
  mode: argv.mode === "production" ? "production" : "development",
  devtool: argv.mode === "production" ? false : "inline-source-map",
  entry: {
    ui: "./src/ui.ts",
    code: "./src/code.ts",
    app: "./src/my-app.ts",
  },
  module: {
    rules: [
      { test: /\.tsx?$/, use: "ts-loader", exclude: /node_modules/ },
      { test: /\.css$/, use: ["style-loader", { loader: "css-loader" }] },
      { test: /\.(png|jpg|gif|webp|svg)$/, loader: "url-loader" },
    ],
  },
  resolve: { extensions: [".ts", ".js"] },
  output: {
    filename: "[name].js",
    path: path.resolve(__dirname, "dist"),
  },
  plugins: [
    new HtmlWebpackPlugin({
      template: path.resolve(__dirname, "ui.html"),
      filename: "ui.html",
      inject: true,
      inlineSource: ".(js|css)$",
      chunks: ["ui"],
    }),
    new HtmlWebpackInlineSourcePlugin(HtmlWebpackPlugin),
  ],
});

Now we need to create the ui for the plugin:

touch ui.html

Open up /src/ui.html and add the following:

<my-app></my-app>

Now we need a manifest file for the figma plugin:

touch manifest.json

Open manifest.json and add the following:

{
  "name": "figma_lit_example",
  "id": "973668777853442323",
  "api": "1.0.0",
  "main": "code.js",
  "ui": "ui.html"
}

Now we need to create our web component:

mkdir src
cd src
touch my-app.ts
touch code.ts
touch ui.ts
cd ..

Open /src/ui.ts and paste the following:

import "./my-app";

Open /src/my-app.ts and paste the following:

import { html, LitElement } from "lit";
import { customElement, query } from "lit/decorators.js";

@customElement("my-app")
export class MyApp extends LitElement {
  @property() amount = "5";
  @query("#count") countInput!: HTMLInputElement;

  render() {
    return html`
      <div>
        <h2>Rectangle Creator</h2>
        <p>Count: <input id="count" value="${this.amount}" /></p>
        <button id="create" @click=${this.create}>Create</button>
        <button id="cancel" @click=${this.cancel}>Cancel</button>
      </div>
    `;
  }

  create() {
    const count = parseInt(this.countInput.value, 10);
    this.sendMessage("create-rectangles", { count });
  }

  cancel() {
    this.sendMessage("cancel");
  }

  private sendMessage(type: string, content: Object = {}) {
    const message = { pluginMessage: { type: type, ...content } };
    parent.postMessage(message, "*");
  }
}

Open code.ts and paste the following:

const options: ShowUIOptions = {
  width: 250,
  height: 200,
};

figma.showUI(__html__, options);

figma.ui.onmessage = msg => {
  switch (msg.type) {
    case 'create-rectangles':
      const nodes: SceneNode[] = [];
      for (let i = 0; i < msg.count; i++) {
        const rect = figma.createRectangle();
        rect.x = i * 150;
        rect.fills = [{ type: 'SOLID', color: { r: 1, g: 0.5, b: 0 } }];
        figma.currentPage.appendChild(rect);
        nodes.push(rect);
      }
      figma.currentPage.selection = nodes;
      figma.viewport.scrollAndZoomIntoView(nodes);
      break;
    default:
      break;
  }

  figma.closePlugin();
};

Building the Plugin 

Now that we have all the code in place we can build the plugin and test it in Figma.

npm run build

Step 1 

Download and open the desktop version of Figma.

Step 2 

Open the menu and navigate to “Plugins > Manage plugins”

Step 3 

Click on the plus icon to add a local plugin.

Click on the box to link to an existing plugin to navigate to the lit-plugin folder that was created after the build process in your source code and select manifest.json.

Step 4 

To run the plugin navigate to “Plugins > Development > figma_lit_example” to launch your plugin.

Step 5 

Now your plugin should launch and you can create 5 rectangles on the canvas.

If everything worked you will have 5 new rectangles on the canvas focused by figma.

WASM Support 

If there is a heavy computation that could benefit from running in WebAssembly the following will ensure that it is hardware accelerated when possible.

Let's add AssemblyScript and some dependencies that will be used for loading the WASM into the figma ui.

npm i @assemblyscript/loader
npm i --D assemblyscript js-inline-wasm
npx asinit .

Confirm yes to the prompt to have it generate the project files and add the following to the scripts in package.json:

"asbuild:untouched": "asc assembly/index.ts --target debug",
"asbuild:optimized": "asc assembly/index.ts --target release",
"asbuild": "npm run asbuild:untouched && npm run asbuild:optimized",
"inlinewasm": "inlinewasm build/optimized.wasm --output src/wasm.ts",

The code that will be used for the WASM is in /assembly/index.ts and it should show the following:

// The entry file of your WebAssembly module.

export function add(a: i32, b: i32): i32 {
  return a + b;
}

Now let's build the wasm module:

npm run asbuild

For the wasm build to be ignored for git add the following to .gitignore:

build

This will generate the wasm and wat files in the build directory, but for figma to load them into the ui it needs to be inlined so run the following command to generate the js from the wasm file:

npm run inlinewasm

This should generate src/wasm.ts with the following:

const encoded = 'AGFzbQEAAAABBwFgAn9/AX8DAgEABQMBAAAHEAIDYWRkAAAGbWVtb3J5AgAKCQEHACAAIAFqCwAmEHNvdXJjZU1hcHBpbmdVUkwULi9vcHRpbWl6ZWQud2FzbS5tYXA=';
export default new Promise(resolve => {
    const decoded = atob(encoded);
    const len = decoded.length;
    const bytes = new Uint8Array(len);
    for (var i = 0; i < len; i++) {
        bytes[i] = decoded.charCodeAt(i);
    }
    resolve(new Response(bytes, { status: 200, headers: { "Content-Type": "application/wasm" } }));
});

Now open up the /src/my-app.ts and update with the following:

import { html, LitElement } from "lit";
import { customElement, property, query } from "lit/decorators.js";

@customElement("my-app")
export class MyApp extends LitElement {
  @property() amount = "5"; // <-- Pass in a value for the number of rectangles to create
  @query("#count") countInput!: HTMLInputElement;

  render() {
    return html`
      <div>
        <h2>Rectangle Creator</h2>
        <!-- Pass in the amount to the input value -->
        <p>Count: <input id="count" value="${this.amount}" /></p>
        ...
      </div>
    `;
  }
  ...
}

This will let us pass in the amount of boxes to create externally.

Now open /src/ui.ts and update it with the following:

import "./my-app";

import wasm from "./wasm"; // <-- Our WASM file to load

WebAssembly.instantiateStreaming(wasm as Promise<Response>).then((obj) => {
  // @ts-ignore
  const value: number = obj.instance.exports.add(2, 4);
  console.log("return from wasm", value);
  const elem = document.querySelector('my-app')! as HTMLElement;
  elem.setAttribute('amount', `${value}`);
});

Now when we build the plugin and run it in figma the amount of boxes will be the result of calling into wasm!

Conclusion 

If you want to learn more about building a plugin in Figma you can read more here and for Lit you can read the docs here.

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