UnusedWebpackPlugin 
A webpack plugin to find unused modules/source files.

Install
npm i --dev unused-webpack-plugin
Usage
const path = require('path');
const UnusedWebpackPlugin = require('unused-webpack-plugin');
module.exports = {
plugins: [
...otherPlugins,
new UnusedWebpackPlugin({
directories: [path.join(__dirname, 'src')],
exclude: ['*.test.js'],
root: __dirname,
}),
],
};
Options
directories
: array of directories where to look for unused source files.exclude
: array of exclude patterns when looking for unused source files.root
: root directory that will be use to display relative paths instead of absolute ones (see below)failOnUnused
: whether or not the build should fail if unused files are found (defaults to false
)useGitIgnore
: whether or not to respect .gitignore
file (defaults to true
)
With root

Without root

Related
If you're not using webpack, check out remnants.