# webpack.config.js
const InjectPlugin = require('webpack-inject-plugin').default;
module.exports = {
    // Other stuff in your webpack config
    plugins: [
        new InjectPlugin(function() {
            return "console.log('Hello World');"
        });
    ]
};

import InjectPlugin, { ENTRY_ORDER } from 'webpack-inject-plugin';
new InjectPlugin(loader, {
    entryName: 'entry name',         //  Limit the injected code to only the entry w/ this name
    entryOrder: ENTRY_ORDER.First    //  Make the injected code be the first entry point
                ENTRY_ORDER.Last     //  Make the injected code be the last entry point
                ENTRY_ORDER.NotLast  //  Make the injected code be second to last. (The last entry module is the API of the bundle. Useful when you don't want to override that.) This is the default.
});

new InjectPlugin(loader, {
  // This will inject code into every entry that's not named `foo`
  entryName: key => key !== 'foo'
});

import InjectPlugin from 'webpack-inject-plugin';
function customLoader(options) {
  return () => {
    return "console.log('My custom code generated from `options`');";
  };
}
export default class MyPlugin {
  constructor(options) {
    this.options = options;
  }
  apply(compiler) {
    new InjectPlugin(customLoader(this.options)).apply(compiler);
  }
}