Using DOM element value as data inside Vue component

Question

I'm trying to add a new feature in a legacy application (built on jQuery) and would like to use Vue.js (v2.6.12) for that.

For example, I have two inputs, and I have a Vue component which displays some data based on the values inside the two inputs (let's say it adds them both). Like this:

Vue.component('output-component', {
  template: `<span> {{outputValue }} </span>`,
  computed: {
    outputValue: function() {
      let value_num1 = document.querySelector('#id_num1').value;
      let value_num2 = document.querySelector('#id_num2').value;
      // I want to access values of #id_num1 and #id_num2 here.
      return value_num1 + value_num2;
    }
  }
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.17/vue.js"></script>

<input type="number" id="id_num1" name="num1" value="1">
<input type="number" id="id_num2" name="num2" value="2">

<output-component/>

Is it even possible to access the DOM values of the inputs this way? And if so, is the above component reactive to changes in the inputs ?

Is there some alternative technique to achieve the same ? (other than of course using jQuery to look for changes in the input and change the output value)

Nick · Accepted Answer · 2020-10-16 11:03:11Z

You need to manually add event listeners to inputs:

Vue.component('output-component', {
  template: `<span> {{outputValue }} </span>`,
  data() {
    return {
      outputValue: null
    }
  },
  methods: {
    recalculateOutputValue() {
      let value_num1 = document.querySelector('#id_num1').value;
      let value_num2 = document.querySelector('#id_num2').value;
      this.outputValue = parseInt(value_num1) + parseInt(value_num2);
    }
  },
  mounted() {
    this.recalculateOutputValue()
    document.querySelector('#id_num1').addEventListener('change', this.recalculateOutputValue);
    document.querySelector('#id_num2').addEventListener('change', this.recalculateOutputValue);
  },
  beforeDestroy() {
    document.querySelector('#id_num1').removeEventListener('change', this.recalculateOutputValue);
    document.querySelector('#id_num2').removeEventListener('change', this.recalculateOutputValue);
  }
});


new Vue({
  el: '#app'
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.17/vue.js"></script>

<input type="number" id="id_num1" name="num1" value="1">
<input type="number" id="id_num2" name="num2" value="2">

<div id="app">
  <output-component/>
</div>

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