Cannot find module '@babel/plugin-proposal-decorators'

问题产生的原因
babel-loader和babel-core版本不对应所产生的，

babel-loader 8.x对应babel-core 7.x
babel-loader 7.x对应babel-core 6.x

如何解决
1、 卸载旧的babel-core
npm un babel-core
2、 安装新的babel-core
npm i -D @babel/core
3、 卸载旧的babel-preset
npm un babel-preset-env
npm un babel-preset-stage-0
4、 安装新的babel-preset
npm i @babel/preset-react
npm i @babel/preset-env
npm i babel-preset-mobx
5、 卸载旧的babel-plugin
npm un babel-plugin-transform-runtime
6、 安装新的babel-plugin
npm install --save-dev @babel/plugin-proposal-object-rest-spread
npm install --save-dev @babel/plugin-transform-runtime
npm install --save @babel/runtime
7、 修改.babelrc文件

{
    "presets": ["@babel/preset-env", "@babel/preset-react", "mobx"],
    "plugins": [
        "@babel/plugin-proposal-object-rest-spread",
        "@babel/plugin-transform-runtime"
    ]
}

如果你按上述命令安装完后，相应的版本应该如下图所示，问题也应该解决了。

"devDependencies": {
    "@babel/core": "^7.2.2",
    "@babel/plugin-proposal-object-rest-spread": "^7.2.0",
    "@babel/plugin-transform-runtime": "^7.2.0",
    "@babel/preset-env": "^7.2.3",
    "@babel/preset-react": "^7.0.0",
    "babel-loader": "^8.0.4",
    "babel-preset-mobx": "^2.0.0",
    "css-loader": "^2.1.0",
    "file-loader": "^3.0.1",
    "popper.js": "^1.14.6",
    "style-loader": "^0.23.1",
    "url-loader": "^1.1.2",
    "webpack": "^4.28.2",
    "webpack-cli": "^3.1.2"
  },
  "dependencies": {
    "@babel/runtime": "^7.2.0",
    "bootstrap": "^4.2.1",
    "jquery": "^3.3.1"
  }