[Feature Request]changing from last state instead of from start-val

[serfend]

<count-to :start-val="0"  :end-val="val" />
<script>
methods:{
    modify() {
      this.val += 100
    }
}
</script>

at first time execute modify() it would from 0 to 100,
how could at second/more times execute modify(), let it from 100 to 200 , instead of 0 to 100 again