在使用serverRenderer打包客户端、服务端后，我先启动了客户端，然后时服务端，打包过程也正常，只不过在渲染服务端页面时，服务端控制台报了一个错：

renderer error ReferenceError: window is not defined
    at Object.module.exports.r (src/store/index.js:229:12)
    at __webpack_require__ (webpack:/webpack/bootstrap 0af5a49ba2806dc9808d:25:0)
    at Object.<anonymous> (src/create-app.js:1:0)
    at __webpack_require__ (webpack:/webpack/bootstrap 0af5a49ba2806dc9808d:25:0)
    at Object.<anonymous> (entry.server.js:21934:70)
    at __webpack_require__ (webpack:/webpack/bootstrap 0af5a49ba2806dc9808d:25:0)
    at module.exports.__webpack_exports__.d (webpack:/webpack/bootstrap 0af5a49ba2806dc9808d:90:0)
    at Object.<anonymous> (entry.server.js:95:10)
    at evaluateModule (C:\Users\xiayi\Desktop\szh-vue-ssr\node_modules\vue-server-renderer\build.dev.js:9303:21)
    at C:\Users\xiayi\Desktop\szh-vue-ssr\node_modules\vue-server-renderer\build.dev.js:9339:17
Error: ReferenceError: window is not defined
    at module.exports (C:\Users\xiayi\Desktop\szh-vue-ssr\server\router\server-render.js:16:11)
    at process._tickCallback (internal/process/next_tick.js:68:7)

说的是项目中使用的window变量未定义，这里涉及一个需求，就是我的Vue项目需要适应屏幕大小，我需要获取window.innerHeight与window.innerWidth，这个情况怎么办？
下面是我处理屏幕自适应的部分的代码：

<template>
  <div :style="fullComputedStyle">
  ....
  </div>
</template>
<script>
  import personalCenter from './components/personalCenter'
  import {mapState} from 'vuex'
  export default {
    name: 'App',
    data() {
      return {
        screenWidth: window.innerWidth,
        screenHeight: window.innerHeight
      }
    },
    components: {
      personalCenter
    },
    computed: {
      fullComputedStyle() {
        return "width: " + this.screenWidth + "px; height: " + this.screenHeight + "px; min-height: 717px;"
      },
      ...mapState(['userId', 'current'])
    },
    created: function () {
      this.init();
    },
    methods: {
      init() {
        this.menuLevel = "1";
        let that = this;
        window.onresize = () => {
          that.screenWidth = window.innerWidth;
          that.screenHeight = window.innerHeight;
        }
      },
      refreshCurrent() {
        console.log(1);
        this.$store.commit("setShowViewer", false);
        this.$nextTick(() => {
          this.$store.commit("setShowViewer", true);
        })
      }
    }
  }
</script>

同时，项目里其他页面也有使用window的地方，怎么才能在全局使用window呢？