Stuck on an issue?

Lightrun Answers was designed to reduce the constant googling that comes with debugging 3rd party libraries. It collects links to all the places you might be looking at while hunting down a tough bug.

And, if you’re still stuck at the end, we’re happy to hop on a call to see how we can help out.

Better error handling for `include` and `exclude` options when option is not an array

See original GitHub issue

Bug Report

I would like to work on a fix!

Current Behavior When setting the exclude option on @babel/preset-env to a string that represents a plugin (with intention to exclude that plugin) babel throws non-descriptive error

 plugins.map is not a function

Moreover, if we provide anything other than array for the options exclude and include, the same error will be thrown, that relates to the way the https://github.com/babel/babel/blob/9a52019019527be8c179ea7c9025fa2355f16170/packages/babel-preset-env/src/normalize-options.js#L78 function handles the input.

Expected behavior/code The expected behavior is to throw a more descriptive error about invalid options provided and maybe to accept valid strings that map to plugins.

Babel Configuration (babel.config.js, .babelrc, package.json#babel, cli command, .eslintrc)

Filename: babel.config.js

module.exports = {
  presets: [
    [
      "@babel/env",
      {
        useBuiltIns: "entry",
        targets: "> 0.01%",
        corejs: 3,
        exclude: "transform-regenerator",
      },
    ],
  ],
};

Environment

System:
    OS: Linux 4.15 Ubuntu 18.04.4 LTS (Bionic Beaver)
  Binaries:
    Node: 10.19.0 - /usr/bin/node
    Yarn: 1.22.4 - /usr/bin/yarn
    npm: 6.13.4 - /usr/bin/npm
  npmPackages:
    @babel/cli: ^7.8.4 => 7.8.4 
    @babel/core: ^7.8.7 => 7.8.7 
    @babel/plugin-transform-modules-amd: ^7.8.3 => 7.8.3 
    @babel/plugin-transform-modules-commonjs: ^7.8.3 => 7.8.3 
    @babel/plugin-transform-runtime: ^7.9.0 => 7.9.0 
    @babel/preset-env: ^7.9.5 => 7.9.5 
    @babel/runtime: ^7.9.2 => 7.9.2 
    @babel/runtime-corejs3: ^7.9.2 => 7.9.2

Possible Solution

Normalize and validate the input before checking here: https://github.com/babel/babel/blob/9a52019019527be8c179ea7c9025fa2355f16170/packages/babel-preset-env/src/normalize-options.js#L85