在VueJs中如何监听window.resize具体该怎么实现？

data: {
 screenWidth: document.body.clientWidth // 这里是给到了一个默认值 （这个很重要）
}

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

  watch: {
   screenWidth (val) {
    this.screenWidth = val
   }
  }

  watch: {
   screenWidth (val) {
    if (!this.timer) {
     this.screenWidth = val
     this.timer = true
     let that = this
     setTimeout(function () {
      // that.screenWidth = that.$store.state.canvasWidth
      console.log(that.screenWidth)
      that.init()
      that.timer = false
     }, 400)
    }
   }
  }