ERROR ReferenceError: Hammer is not defined (Help me)

// Work around for https://github.com/angular/angular-cli/issues/7200

const path = require('path');

const webpack = require('webpack');

const nodeExternals = require('webpack-node-externals');

module.exports = {

  mode: 'none',

  entry: {

    // This is our Express server for Dynamic universal

    server: './server.ts',

    // This is an example of Static prerendering (generative)

  },

  target: 'node',

  resolve: { extensions: ['.ts', '.js'] },

  // Make sure we include all node_modules etc

  externals: [/node_modules/, nodeExternals({

    whitelist: [

        /^@agm\/core/,

        /^hammerjs/

      ]

  })],

  output: {

    // Puts the output at the root of the dist folder

    path: path.join(__dirname, 'dist'),

    filename: '[name].js'

  },

  module: {

    rules: [

      { test: /\.ts$/, loader: 'ts-loader' },

      {

        // Mark files inside `@angular/core` as using SystemJS style dynamic imports.

        // Removing this will cause deprecation warnings to appear.

        test: /[\/\\]@angular[\/\\]core[\/\\].+\.js$/,

        parser: { system: true },

      },

    ]

  },

  plugins: [

    new webpack.ContextReplacementPlugin(

      // fixes WARNING Critical dependency: the request of a dependency is an expression

      /(.+)?angular(\\|\/)core(.+)?/,

      path.join(__dirname, 'src'), // location of your src

      {} // a map of your routes

    ),

    new webpack.ContextReplacementPlugin(

      // fixes WARNING Critical dependency: the request of a dependency is an expression

      /(.+)?express(\\|\/)(.+)?/,

      path.join(__dirname, 'src'),

      {}

    )

  ]

}