data: {
 screenWidth: document.body.clientWidth // 這里是給到了一個默認值 （這個很重要）
}

 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)
 }
 }
 }