npm i jquery --save

//在main.js中引入
import jQuery from 'jquery
Vue.prototype.$ = jQuery;

在 build/webpack.base.conf.js
引入
var webpack = require('webpack')


module.exports = {
  entry: {
    app: './src/main.js'
  },
  output: {
    path: config.build.assetsRoot,
    filename: '[name].js',
    publicPath: process.env.NODE_ENV === 'production'
      ? config.build.assetsPublicPath
      : config.dev.assetsPublicPath
  },
  resolve: {
    extensions: ['.js', '.vue', '.json'],
    alias: {
      'vue$': 'vue/dist/vue.esm.js',
      '@': resolve('src')
    }
  },
//添加這個
  plugins: [
      new webpack.ProvidePlugin({
          $: "jquery",
          jQuery: "jquery"
      })
   ],
...其他代碼
}`