如果我们更改了源代码，而不像每次都要运行npm run build，该如何办呢？

1、更改package.json文件，scripts追加"watch": "webpack --watch"开启webpack watch模式

{
  "name": "webpack-demo",
  "version": "1.0.0",
  "description": "",
  "private": true,
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1",
    "build": "webpack",
    "watch": "webpack --watch"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "clean-webpack-plugin": "^2.0.2",
    "css-loader": "^2.1.1",
    "csv-loader": "^3.0.2",
    "file-loader": "^3.0.1",
    "html-webpack-plugin": "^3.2.0",
    "style-loader": "^0.23.1",
    "webpack": "^4.32.0",
    "webpack-cli": "^3.3.2",
    "xml-loader": "^1.2.1"
  },
  "dependencies": {
    "lodash": "^4.17.11"
  }
}

2、watch模式运行

npm run watch

3、运行效果

4、修改print.js文件

export default function print() {
    // console.error('code find a error!'); 修改前
    console.log('code was updated!');
}

5、刷新页面，运行效果如下：