Google Apps Script and ES Modules

Currently, Google Apps Script does not support ES modules - and any usage of export/import 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 in ./src will end up in the ./build-folder. 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
!build/*.js

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

This should be enough to start developing a project using ES Modules.