Vue.js如何监听window窗口尺寸变化

data() {
    return {
       screenWidth: document.body.clientWidth,//初始化宽度
    }
},

var _this = this
window.onresize = () => {
        return (() => {
            _this .screenWidth = document.body.clientWidth
        })()
      }

screenWidth(){
        if (!this.timer) {
            this.timer = true
            let _this= this
            setTimeout(function () {
              ... (执行的语句)
              _this.timer = false
            }, 500)
        }
      }

data:{
    screenWidth: document.body.clientWidth
}

mounted () {
    const that = this
    window.onresize = () => {
        return (() => {
            window.screenWidth = document.body.clientWidth
            that.screenWidth = window.screenWidth
        })()
    }
}

watch:{
    screenWidth(val){
        // 为了避免频繁触发resize函数导致页面卡顿，使用定时器
        if(!this.timer){
            // 一旦监听到的screenWidth值改变，就将其重新赋给data里的screenWidth
            this.screenWidth = val
            this.timer = true
            let that = this
            setTimeout(function(){
                // 打印screenWidth变化的值
                console.log(that.screenWidth)
                that.timer = false
            },400)
        }
    }
}