这几天在学习vue，到了其中的网络请求部分，由于是前后端分离结构，所以自然就出现了跨域问题。
我的前端运行在8080端口, 后端运行在8181端口
我的vue.config.js配置如下

const path = require('path')
const webpack = require('webpack')
const GitRevisionPlugin = require('git-revision-webpack-plugin')
const GitRevision = new GitRevisionPlugin()
const buildDate = JSON.stringify(new Date().toLocaleString())
const createThemeColorReplacerPlugin = require('./config/plugin.config')

function resolve (dir) {
  return path.join(__dirname, dir)
}

// check Git
function getGitHash () {
  try {
    return GitRevision.version()
  } catch (e) {}
  return 'unknown'
}

const isProd = process.env.NODE_ENV === 'production'

const assetsCDN = {
  // webpack build externals
  externals: {
    vue: 'Vue',
    'vue-router': 'VueRouter',
    vuex: 'Vuex',
    axios: 'axios'
  },
  css: [],
  // https://unpkg.com/browse/vue@2.6.10/
  js: [
    '//cdn.jsdelivr.net/npm/vue@2.6.10/dist/vue.min.js',
    '//cdn.jsdelivr.net/npm/vue-router@3.1.3/dist/vue-router.min.js',
    '//cdn.jsdelivr.net/npm/vuex@3.1.1/dist/vuex.min.js',
    '//cdn.jsdelivr.net/npm/axios@0.19.0/dist/axios.min.js'
  ]
}

// vue.config.js
const vueConfig = {



  configureWebpack: {
    // webpack plugins
    plugins: [
      // Ignore all locale files of moment.js
      new webpack.IgnorePlugin(/^\.\/locale$/, /moment$/),
      new webpack.DefinePlugin({
        APP_VERSION: `"${require('./package.json').version}"`,
        GIT_HASH: JSON.stringify(getGitHash()),
        BUILD_DATE: buildDate
      })
    ],
    // if prod, add externals
    externals: isProd ? assetsCDN.externals : {}
  },

  chainWebpack: (config) => {
    config.resolve.alias
      .set('@$', resolve('src'))

    const svgRule = config.module.rule('svg')
    svgRule.uses.clear()
    svgRule
      .oneOf('inline')
      .resourceQuery(/inline/)
      .use('vue-svg-icon-loader')
      .loader('vue-svg-icon-loader')
      .end()
      .end()
      .oneOf('external')
      .use('file-loader')
      .loader('file-loader')
      .options({
        name: 'assets/[name].[hash:8].[ext]'
      })

    // if prod is on
    // assets require on cdn
    if (isProd) {
      config.plugin('html').tap(args => {
        args[0].cdn = assetsCDN
        return args
      })
    }
  },

  css: {
    loaderOptions: {
      less: {
        modifyVars: {
          // less vars，customize ant design theme

          // 'primary-color': '#F5222D',
          // 'link-color': '#F5222D',
          'border-radius-base': '2px'
        },
        // DO NOT REMOVE THIS LINE
        javascriptEnabled: true
      }
    }
  },

  devServer: {
    // development server port 8000
    port: 8080,
    open: true,
    overlay: {
      warning: false,
      errors: true
    },
    // If you want to turn on the proxy, please remove the mockjs /src/main.jsL11
    proxy: {
      '/api': {
        target: 'http://localhost:8181/api',
        changOrigin: true,  //允许跨域
        secure: false,  // 如果是https接口，需要配置这个参数
        ws: true,   //如果要代理 websockets，配置这个参数
        pathRewrite:{
          '^/api':''
        }
      }
    }
  },

  // disable source map in production
  productionSourceMap: false,
  lintOnSave: false,//undefined
  devServer: {//这里多了一个
	   overlay: {  
	      warning: false,
	      errors: true
	    }
  },
    // lintOnSave: false, 
  // babel-loader no-ignore node_modules/*
  transpileDependencies: []
}

// preview.pro.loacg.com only do not use in your production;
if (process.env.VUE_APP_PREVIEW === 'true') {
  console.log('VUE_APP_PREVIEW', true)
  // add `ThemeColorReplacer` plugin to webpack plugins
  vueConfig.configureWebpack.plugins.push(createThemeColorReplacerPlugin())
}

module.exports = vueConfig

运行npm run serve 发现仍然出现404错误，几经查找, 后来终于找到来原因…
问题的原因可能有以下几种.

1:重新运行 npm run serve, 尤其是改来vue.config.js文件的内容, 最好重启一下
2:浏览器里直接访问目标地址 , 测试接口是否能够正常访问
3.检查一下devServer属性是不是有两个? 我的就是这个问题导致的.