npm install content-replace-webpack-plugin --save--dev

var ContentReplacePlugin = require('content-replace-webpack-plugin')
 
module.exports = {
    entry:{
        index:"./index.js"
    },
    module:{
        loaders:[
            ...
        ]
    },
    output:{
        path:'./dist',
        filename:'[name].min.js'
    },
    plugins:[
        new ContentReplacePlugin({
          external: ['path/to/other/file'], // other files which not in webpack assets
          chunks: ['index'],
          rules: {
            '.js': content => content.replace('/foo', '/bar')
          }
        })
    ]
}