Edit in JSFiddle

new Vue({
    el: "#app",
    data: {
        output: "111",
        selected: "YYYY-MM-DD",
    },
    computed: {
    	date(){
      	return new Date().toISOString().slice(0,10).replace(/\-/g, '');
      }
    },
    methods: {
        convert(type){
        	this.selected = type;
        	const res = this.date.replace(/(\d{4})(\d{1,2})(\d{1,2})/, ($f,$1,$2,$3)=>{
          	return type.replace('YYYY', $1).replace('MM', $2).replace('DD', $3);
          });
          this.output = res;
        }
    },
    mounted() {
        this.convert(this.selected);
    }
})