webpack 怎么直接实时编译输出文件

新建一个server服务用他来启动监听webpack.config.js
用node server.js启动服务

var webpack = require('webpack');
var webpackDevMiddleware = require("webpack-dev-middleware");
var webpackDevServer = require('webpack-dev-server');
var config = require("./webpack.config.js");

config.entry.index.unshift('webpack/hot/dev-server');
config.entry.index.unshift('webpack-dev-server/client?http://localhost:8080');

var compiler = webpack(config);

var server = new webpackDevServer(compiler, {
historyApiFallback: true,
hot: true,
inline: true,
stats: 'errors-only',
host: "localhost",
port: "8080",
});
server.listen(8080);