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; }...