Debounce computed properties/getters in Vue

Question

I can't seem to debounce (lodash) computed properties or vuex getters. The debounced functions always return undefined.

https://jsfiddle.net/guanzo/yqk0jp1j/2/

HTML:

<div id="app">
  <input v-model="text">
  <div>computed: {{ textComputed }} </div>
  <div>debounced: {{ textDebounced }} </div>
</div>

JS:

new Vue({
    el:'#app',
  data:{
    text:''
  },
  computed:{
    textDebounced: _.debounce(function(){
      return this.text
    },500),
    textComputed(){
        return this.text
    }
  }

})

Answer 1

As I mention in my comment, debouncing is an inherently asynchronous operation, and so cannot return a value. Depending on your needs, you might want to debounce on the input side. There will be no difference between the value in text and that in textComputed, but if you v-model="textComputed", the value setting will be debounced.

If you specifically want a debounced version of a variable, mrogers has given a good solution.

var x = new Vue({
  el: '#app',
  data: {
    text: 'start'
  },
  computed: {
    textComputed: {
      get() {
        return this.text;
      },
      set: _.debounce(function(newValue) {
        this.text = newValue;
      }, 500)
    }
  }
})

<script src="//cdnjs.cloudflare.com/ajax/libs/vue/2.3.4/vue.min.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.4/lodash.js"></script>
<div id="app">
  <div>
    Debounced input:
    <input v-model="textComputed">
  </div>
  <div>
    Immediate input:
    <input v-model="text">
  </div>
  <div>computed: {{ textComputed }} </div>
  <div>debounced: {{ text }} </div>
</div>

Answer 2

1. Simple
2. No external dependencies (like _.debounce)
3. Tailored for Vue

import Vue from 'vue'

// Thanks to https://github.com/vuejs-tips/v-debounce/blob/master/debounce.js
function debounce(fn, delay) {
  var timeoutID = null
  return function () {
    clearTimeout(timeoutID)
    var args = arguments
    var that = this
    timeoutID = setTimeout(function () {
      fn.apply(that, args)
    }, delay)
  }
}

function debouncedProperty(delay) {
  let observable = Vue.observable({ value: undefined });
  return {
    get() { return observable.value; },
    set: debounce(function (newValue) { observable.value = newValue; }, delay)
  }
}

// component
export default {
  computed: {
    myProperty: debouncedProperty(300),
  },
}

Answer 3

I don't have any insight as to why the debounce function doesn't work on a computed property. However, an alternative solution is to put the debounce on a function in the methods section and call it via a watch.

https://jsfiddle.net/vsc4npv3/

HTML:

<div id="app">
<input v-model="text">
<div>computed: {{ textComputed }} </div>
<div>debounced: {{ debouncedText }} </div>
</div>

JavaScript:

var x = new Vue({
    el:'#app',
  data:{
    text:'',
    debouncedText: ''
  },
  watch: {
    text: function (val) {
        this.debouncer();
    }
  },
  computed:{
    textComputed(){
        return this.text;
    }
  },
  methods: {
    debouncer: _.debounce(function(){
      this.debouncedText = this.text;
    },500)
  }

})