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    <div id="demo">

      <div v-for='(item, index) in arr'>
        <input @change="updateValue(item, $event, 'x')" placeholder="x value" :value="item.x">
        <input @change="updateValue(item, $event, 'y')" placeholder="y value" :value="item.y">
        <hr>
      </div>
      <code>{{ arr | json }}</code>
    </div>

    var data = {

          arr: [
          	{
            	id: 1,
              name: 'a',
              x: 666
            }, 
            {
            	id: 2,
              name: 'b'
            }
          ]

    }

    var demo = new Vue({
        el: '#demo',
        data: data,
        methods: {
        	updateValue: function(item, event, key) {
          	let val = event.target.value;
		        Vue.set(item, key, val);
          }
        }
    })