computed

    let myInput = {
        template:`  <div>
                        <input v-model="msg">
                        <br>
                        <span>{{changeMsg}}</span>
                    </div>`,
        data() {
            return {
                msg:‘hello‘
            }
        },
        computed:{
            changeMsg() {
                return this.msg.split(‘‘).join()
            }
        }
    }
    new Vue({
        el: "#app",
        components:{
            myInput
        }
    })