data:

defaultPhoneHeight:'',
nowPhoneHeight:''

mounted:

mounted(){
    this.defaultPhoneHeight = window.innerHeight
    window.onresize = ()=>{
        this.nowPhoneHeight = window.innerHeight
    }
},

destroyed:
destroyed() {

window.onresize = null

}

watch:

    nowPhoneHeight:function(){
        if(this.defaultPhoneHeight != this.nowPhoneHeight){
            //手机键盘被唤起了
            alert('手机键盘被唤起了')    
          }else{
               //手机键盘被关闭了。
        // alert('手机键盘被关闭了')                    
             }
     }