esmodules.md

ES Modules

Currently, Google Apps Script does not support ES modules. Hence the typical export/import pattern cannot be used and will fail.

One way of handling this is to use rollup.js to bundle your project into one single JavaScript file.

The trick here is to make sure not to export any functions in your entry point code, e.g. index.ts, and to prevent any generation of export statement in the final bundle (see the custom rollup plugin in the rollup.config.js below).

import { babel } from "@rollup/plugin-babel";
import { nodeResolve } from "@rollup/plugin-node-resolve";

const extensions = [".ts", ".js"];

const preventThreeShakingPlugin = () => {
    return {
      name: 'no-threeshaking',
      resolveId(id, importer) {
        if (!importer) {
            // let's not theeshake entry points, as we're not exporting anything in Apps Script files
          return {id, moduleSideEffects: "no-treeshake" }
        }
        return null;
      }
    }
  }

export default {
  input: "./src/index.ts",
  output: {
    dir: "build",
    format: "esm",
  },
  plugins: [
    preventThreeShakingPlugin(),
    nodeResolve({
      extensions,
    }),
    babel({ extensions, babelHelpers: "runtime" }),
  ],
};

In order to use babel to transpile the code, be sure to add a babel.config.js to the project:

module.exports = {
  presets: [
    [
      // ES features necessary for user's Node version
      require("@babel/preset-env").default,
      {
        targets: {
          node: "current",
        },
      },
    ],
    [require("@babel/preset-typescript").default],
  ],
};

In the above example, the resulting bundle created by transpiling the entry point, i.e. ./src/index.ts, will end up as ./build/index.js. To make sure Clasp picks the right files to push, a .claspignore-file must be added to the project:

# ignore all files…
**/**

# except the extensions…
!appsscript.json
# and our transpiled code
!build/*.js

# ignore even valid files if in…
.git/**
node_modules/**

Now you can push using your normal clasp push-command!

This should be enough to start developing a project using ES Modules. A complete example repo can be cloned from atti187/esmodules.