今天有空，就去梳理一下webpack的基础知识和配置，然后找了一篇博文跟着步骤走，到‘使用webpack-dev-server’这一步时，运行npm start报错：Cannot find module 'webpack/schemas/WebpackOptions.json'

博文教程：https://segmentfault.com/a/1190000010871559#articleHeader15

我的配置如下：

packge.json

{
  "name": "webpack-demo",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "build": "webpack",
    "start": "webpack-dev-server --open"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "clean-webpack-plugin": "^0.1.19",
    "css-loader": "^0.28.11",
    "file-loader": "^1.1.11",
    "html-webpack-plugin": "^3.2.0",
    "style-loader": "^0.21.0",
    "webpack": "^3.4.1",
    "webpack-cli": "^2.1.4",
    "webpack-dev-server": "^3.1.4" //关键第一句
  },
  "dependencies": {
    "lodash": "^4.17.10"
  }
}

webpack.config.js

const path = require('path');
const HtmlWebpackPlugin = require('html-webpack-plugin');
const CleanWebpackPlugin = require('clean-webpack-plugin');
// const webpack = require('webpack');

module.exports = {
    devtool: 'inline-cheap-module-source-map',
    entry: {
        app: './src/index.js',
        print: './src/print.js'
    },
    output: {
        filename: '[name].bundle.js',
        path:path.resolve(__dirname, 'dist')
    },
    module: {
        rules: [
            {
                test: /\.css$/,
                use: [
                    'style-loader',
                    'css-loader'
                ]
            },
            {
                test: /\.(png|svg|jpg|gif)$/,
                use: [
                    'file-loader'
                ]
            },
            {
                test: /\.(woff|woff2|eot|ttf|otf)$/,
                use: [
                    'file-loader'
                ]
            }
        ]
    },
    devServer:{
        contentBase: path.resolve(__dirname, 'dist'),//关键第二句
    },
    plugins: [
        new HtmlWebpackPlugin({
            title:'webpack demo',
            filename:'index.html'
        }),
        new CleanWebpackPlugin(['dist']),
    ]
}

开始网上的很多解决方案都不是我的问题所在，因为我的webpack全局、局部都安装好了。后来猜测：我的webpack版本是参照教程里面安装的3.4.1，而webpack-dev-server是默认安装的最新的3.1.4，报错说找不到WebpackOptions.json文件，有可能是版本不配套，现在webpack最新版本是4.9.1了，最新的webpack应该有WebpackOptions.json文件，所以，3.1.4的webpack-dev-server是跟4.X.X的webpack配套的，所以测试：

将webpack-dev-server降级：

npm uninstall webpack-dev-server

npm i --save-dev webpack-dev-server@2.9.7

再运行命令：npm start

真的成功了！

所以我现在的package.json：

{
  "name": "webpack-demo",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "build": "webpack",
    "start": "webpack-dev-server --open"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "clean-webpack-plugin": "^0.1.19",
    "css-loader": "^0.28.11",
    "file-loader": "^1.1.11",
    "html-webpack-plugin": "^3.2.0",
    "style-loader": "^0.21.0",
    "webpack": "^3.4.1",
    "webpack-cli": "^2.1.4",
    "webpack-dev-server": "^2.9.7"
  },
  "dependencies": {
    "lodash": "^4.17.10"
  }
}

总结：这个错误网上搜索的结果，大部分是说因为webpack没局部安装，或者start命令配置错误，而实际上我的报错原因是，webpack和webpack-dev-server版本不配套导致，所以有时候报错要能静下来自己分析一下原因也是好的。另外，问题是解决了，要证明我的猜测完全正确，得下次安装了webpack4，看看如果有WebpackOptions.json文件，那就猜对了，今天先接着把3弄完。