//v-on:click 简写@click
<div id="div1">
  {{a}}
  <input type="button" value="+1" v-on:click="fn(5)">
  <input type="button" value="+1" @click="fn(5)">
</div>
let vm=new Vue({
    el: '#div1',
    data: {
      a: 12
    },
    methods: {
      fn(n){
        this.a+=n;
      }
    }
});

<div id="div1">
	<input type="text" v-model="n1">+
	<input type="text" v-model="n2">=
	{{parseInt(n1)+parseInt(n2)}}
</div>

let vm=new Vue({
	el: '#div1',
	data: {
		n1: 0, n2: 0
	}
});

<div id="div1">
	<input type="text" v-model="n1">+
	<input type="text" v-model="n2">=
	{{sum()}}
</div>

let vm=new Vue({
	el: '#div1',
	data: {
		n1: 0, n2: 0
	},
	methods: {
		sum(){
			return parseInt(this.n1)+parseInt(this.n2);
		}
	}
});