SOURCE

<script src="https://cdn.jsdelivr.net/npm/vue@2/dist/vue.js"></script>
<div id="app">
    <button v-on:click="add">
        +
    </button>
    <span>
        {{num}}
    </span>
    <button v-on:click="sub">
        -
    </button>
</div>

<script>
    var app = new Vue({
        el:"#app",
        data:{
            num:1
        },
        methods:{
            add:function(){
                this.num++;
                if(this.num>10){
                    alert("Maximum");
                    this.num = 10;
                }

            },
            sub:function(){
                this.num--;
                

                if(this.num<1){
                    alert("Minimum");
                    this.num = 1;
                }
            }
        }
    })
</script>