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mock使用场景：后端接口的开发速度跟不上前端的进度， 而前端要实现业务还必须依赖数据，前端为了保证开发进度就需要自己去创建mock数据 ，才能保证业务正常开发。

mock的数据是我们自己定义的假数据，常称为mock数据

实现方式

线上mock

https://www.fastmock.site/

手动写

使用步骤

1. 下载包

npm i axios mockjs 

2.引如mock文件

mock/mock-server.js

const chokidar = require('chokidar')
const bodyParser = require('body-parser')
const chalk = require('chalk')
const path = require('path')
const Mock = require('mockjs')

const mockDir = path.join(process.cwd(), 'mock')

function registerRoutes(app) {
  let mockLastIndex
  const { mocks } = require('./index.js')
  const mocksForServer = mocks.map(route => {
    return responseFake(route.url, route.type, route.response)
  })
  for (const mock of mocksForServer) {
    app[mock.type](mock.url, mock.response)
    mockLastIndex = app._router.stack.length
  }
  const mockRoutesLength = Object.keys(mocksForServer).length
  return {
    mockRoutesLength: mockRoutesLength,
    mockStartIndex: mockLastIndex - mockRoutesLength
  }
}

function unregisterRoutes() {
  Object.keys(require.cache).forEach(i => {
    if (i.includes(mockDir)) {
      delete require.cache[require.resolve(i)]
    }
  })
}

// for mock server
const responseFake = (url, type, respond) => {
  return {
    // url: new RegExp(`${process.env.VUE_APP_BASE_API}${url}`),
    url: new RegExp(`${url}`),
    type: type || 'get',
    response(req, res) {
      console.log('request invoke:' + req.path)
      res.json(Mock.mock(respond instanceof Function ? respond(req, res) : respond))
    }
  }
}

module.exports = app => {
  // parse app.body
  // https://expressjs.com/en/4x/api.html#req.body
  app.use(bodyParser.json())
  app.use(bodyParser.urlencoded({
    extended: true
  }))

  const mockRoutes = registerRoutes(app)
  var mockRoutesLength = mockRoutes.mockRoutesLength
  var mockStartIndex = mockRoutes.mockStartIndex

  // watch files, hot reload mock server
  chokidar.watch(mockDir, {
    ignored: /mock-server/,
    ignoreInitial: true
  }).on('all', (event, path) => {
    if (event === 'change' || event === 'add') {
      try {
        // remove mock routes stack
        app._router.stack.splice(mockStartIndex, mockRoutesLength)

        // clear routes cache
        unregisterRoutes()

        const mockRoutes = registerRoutes(app)
        mockRoutesLength = mockRoutes.mockRoutesLength
        mockStartIndex = mockRoutes.mockStartIndex

        console.log(chalk.magentaBright(`\n > Mock Server hot reload success! changed  ${path}`))
      } catch (error) {
        console.log(chalk.redBright(error))
      }
    }
  })
}

mock/new.js

module.exports = [
    {
      url: '/news/list',
      type: 'get',
      response: config => {
        return {
          code: 20000,
          data: {
            total: 3,
            items: ['a', 'b', 'c']
          }
        }
      }
    }
  ]

mock/index.js

const Mock = require('mockjs')
const { param2Obj } = require('./utils')

const user = require('./user')
const table = require('./table')
const news = require('./new')

const mocks = [
  ...user,
  ...table,
  ...news
]

// for front mock
// please use it cautiously, it will redefine XMLHttpRequest,
// which will cause many of your third-party libraries to be invalidated(like progress event).
function mockXHR() {
  // mock patch
  // https://github.com/nuysoft/Mock/issues/300
  Mock.XHR.prototype.proxy_send = Mock.XHR.prototype.send
  Mock.XHR.prototype.send = function() {
    if (this.custom.xhr) {
      this.custom.xhr.withCredentials = this.withCredentials || false

      if (this.responseType) {
        this.custom.xhr.responseType = this.responseType
      }
    }
    this.proxy_send(...arguments)
  }

  function XHR2ExpressReqWrap(respond) {
    return function(options) {
      let result = null
      if (respond instanceof Function) {
        const { body, type, url } = options
        // https://expressjs.com/en/4x/api.html#req
        result = respond({
          method: type,
          body: JSON.parse(body),
          query: param2Obj(url)
        })
      } else {
        result = respond
      }
      return Mock.mock(result)
    }
  }

  for (const i of mocks) {
    Mock.mock(new RegExp(i.url), i.type || 'get', XHR2ExpressReqWrap(i.response))
  }
}

module.exports = {
  mocks,
  mockXHR
}

3.配置vue.config.js

'use strict'

module.exports = {
  /**
   * You will need to set publicPath if you plan to deploy your site under a sub path,
   * for example GitHub Pages. If you plan to deploy your site to https://foo.github.io/bar/,
   * then publicPath should be set to "/bar/".
   * In most cases please use '/' !!!
   * Detail: https://cli.vuejs.org/config/#publicpath
   */
  publicPath: './',
  outputDir: 'dist',
  assetsDir: 'static',
  productionSourceMap: false,
  devServer: {
    port: 8001,
    open: true,
    overlay: {
      warnings: false,
      errors: true
    },
    before: require('./mock/mock-server.js') // 重点
  }
}

4. 去页面中使用：

<template>
  <div id="app">
    <button @click="send"></button>
  </div>
</template>
import axios from 'axios'
export default {
  name: 'App',
  methods: {
    send() {
      const url = "/api/news/list" 
      axios({url}).then(res => {console.log(res)})
    }
  },
}
</script>