const app = new Vue({
el:'#app',
data:{
counter:1,
show:true
},
methods: {
add:function(){
this.counter++
},
sub:function(){
if(this.counter>0){
this.counter--
}else{
this.counter = 0
this.show = !this.show
}
}
}
})
<div id="app">
<div>
<button v-on:click="add">+</button>
<span>{{counter}}</span>
<button @click="sub" v-show="show">-</button>
</div>
</div>