Babel and Webpack are throwing "Can't resolve 'regenerator-runtime/runtime'"

Question

I'm working on a browser-based project that needs to be IE11-compatible (sigh). Webpack is choking on async/await. Here is my console's output:

Based on your code and targets, added regenerator-runtime.
...
Module not found: Error: Can't resolve 'regenerator-runtime/runtime'

I've looked at many SO questions similar to mine, without luck. Many recommend using @babel/polyfill which I am avoiding since it has been deprecated.

What is causing this issue? I expect it could be fixed by manually importing regenerator-runtime/runtime, but it seems one of the main selling points of babel-env is NOT having to manually import polyfills, so I assume I'm missing a step. Thank you!

Here is what I am attempting to run, which is being imported into another file:

class Fetcher {
    constructor() {
        this.form = document.querySelector('form');
        this.form.addEventListener('submit', this.onSubmit.bind(this));
    }

    async onSubmit(event) {
        event.preventDefault();

        const apiResponse = await fetch(`${WP_url}/api`);
        const apiJson = await apiResponse.json();
        console.log(apiJson);
    }
}
export default Fetcher;

webpack.config.js:

const path = require('path');

function pathTo(filepath) {
    return path.join(__dirname, filepath);
}

module.exports = function(env, argv) {
    const isProd = Boolean(argv.mode === 'production');

    const config = {
        entry: {
            index: [
                pathTo('index.js'),
            ],
        },
        externals: {
            jquery: 'jQuery',
        },
        module: {
            rules: [
                {
                    test: /\.js$/,
                    exclude: /node_modules/,
                    loader: 'babel-loader',
                    options: {
                        presets: [
                            [
                                '@babel/preset-env',
                                {
                                    corejs: 3,
                                    debug: true,
                                    targets: {
                                        browsers: [
                                            'IE 11',
                                        ],
                                    },
                                    useBuiltIns: 'usage',
                                },
                            ],
                        ],
                    },
                },
            ],
        },
        optimization: {
            minimize: isProd,
        },
        output: {
            filename: '[name].js',
            path: pathTo('web'),
        },
    };

    return config;
};

package.json

{
  "private": true,
  "dependencies": {
    "core-js": "^3.4.1",
    "focus-within-polyfill": "^5.0.5"
  },
  "devDependencies": {
    "@babel/core": "^7.7.2",
    "@babel/preset-env": "^7.7.1",
    "babel-eslint": "^10.0.3",
    "babel-loader": "^8.0.6",
    "css-loader": "^3.2.0",
    "eslint": "^6.6.0",
    "mini-css-extract-plugin": "^0.8.0",
    "node-sass": "^4.13.0",
    "sass-loader": "^8.0.0",
    "webpack": "^4.41.2",
    "webpack-cli": "^3.3.10"
  },
  "scripts": {
    "dev": "webpack --mode=development --display-modules",
    "dev:watch": "npm run dev -- --watch",
    "prod": "webpack --mode=production --display-modules",
    "prod:watch": "npm run prod -- --watch"
  }
}

Answer 1

Simply running npm i regenerator-runtime fixed it, actually.

With useBuiltIns: 'usage', having all the import statements wasn't necessary I guess.

¯\_(ツ)_/¯

Answer 2

I started getting this error when added transpileDependencies: ['openplayerjs'], to my vue.config.js, as Babel with @vue/cli-plugin-babel/preset won't touch dependencies in node_modules, go figure why. Installing regenerator-runtime did not help, and I thought the issue lied in Yarn's pnp modules:

This dependency was not found:

* regenerator-runtime/runtime.js in /Volumes/Backup/home/Documents/.yarn/unplugged/openplayerjs-npm-2.9.3-aa4692035d/node_modules/openplayerjs/dist/esm/media.js, /Volumes/Backup/home/Documents/.yarn/unplugged/openplayerjs-npm-2.9.3-aa4692035d/node_modules/openplayerjs/dist/esm/media/ads.js and 1 other

To install it, you can run: npm install --save regenerator-runtime/runtime.js

so I tried unplugging everything via yarn unplug <module_name>, still did not work.

Eventually changing useBuiltIns: 'usage' to useBuiltIns: 'entry' in babel.config.js solved it straight away.

Answer 3

Just add import 'regenerator-runtime/runtime' in the file where you have the async/await.

Answer 4

In my case, your answer wasn't enough and I needed to set babel sourceType to unambiguous as suggested here to allow a correct compilation of the project. This option was required because the @babel/runtime/regenerator/index.js file exports its reference using module.exports = require("regenerator-runtime"); that breaks ES6 compilation.

Another useful note resolving a similar but unrelated compilation issue was to use /node_modules\/(css-loader|@babel|core-js|promise-polyfill|webpack|html-webpack-plugin|whatwg-fetch)\// as exclude for the babel rule to avoid resolution loops without loosing external libraries compilation (when necessary) as suggested here.

TL;DR

In your specific case the babel rule would become:

{
  test: /\.js$/,
  exclude: /node_modules/,
  loader: 'babel-loader',
  options: {
    sourceType: 'unambiguous',
    presets: [
      ['babel/preset-env', {
        corejs: 3,
        debug: true,
        targets: {
          browsers: [ 'IE 11', ],
        },
        useBuiltIns: 'usage',
      }],
    ],
  },
},