Using the spread operator in a component's render function could potentially lead to an endless update loop

Question

Using the spread operator in a component's render function could potentially lead to an endless update loop

Although this issue has been addressed before in a discussion about the "You may have an infinite update loop in a component render function" warning in Vue component, the solution provided did not resolve my problem.

I am seeking assistance to understand what might be causing the issue in my case.

<template>
  <div>
    <template v-for="listing in sortedListings">
      <listing
        :key="listing.uuid"
        :listing="listing"
        :highlight-color="listing.highlight ? getHighlightColor() : null"
      />
    </template>
  </div>
</template>

<script>
import Listing from '@/components/Listing'
export default {
  components: {
    Listing,
  },
  data: function () {
    return {
      highlightColors: this.getHighlightColors(),
      listings: [
        {
          uuid: '658f325f-33c8-455b-98f6-27eb4eaa16a0',
          title: 'Cursus Nullam Amet Tortor',
          location: 'Remote',
          url: 'http://example.net/birds',
          hours_week: 20,
          tags: ['django', 'python', 'flask'],
          logo: 'https://logo.clearbit.com/apple.com',
          company_name: 'Apple',
          show_logo: 1,
          highlight: 0,
          stick_top: 0,
        },
        // additional listing items...
      ],
    }
  },
  computed: {
    sortedListings: function () {
      return [...this.listings].sort(function (a, b) {
        return b.stick_top - a.stick_top
      })
    },
  },
  methods: {
    getListings: async function () {},
    getHighlightColors: function () {
      return this.shuffleArray([
        '#E3F2FD',
        '#E8EAF6',
        '#FFEBEE',
        '#E0F2F1',
        '#E8F5E9',
        '#FFF3E0',
        '#FFFDE7',
      ])
    },
    getHighlightColor: function () {
      if (this.highlightColors.length === 0) {
        this.highlightColors = this.getHighlightColors()
      }
      return this.highlightColors.shift()
    },
  },
  mounted: function () {
    this.getListings()
  },
}
</script>

In the computed property sortedListings, I have already implemented [...this.listings].

javascript vue.js

Answer 1

Answer №1

When using the spread operator to copy an array, it's important to note that it doesn't create a deep clone. Additionally, if the sort method is used on the original array within a computed property, it can lead to an infinite loop. To avoid this issue, consider adding a method for deep cloning objects like the one mentioned in this reference:

...

 computed: {
    sortedListings: function () {
      return this.deepCopy(this.listings).sort(function (a, b) {
        return b.stick_top - a.stick_top
      })
    },
  },
  methods: {
   deepCopy(src) {
     let target = Array.isArray(src) ? [] : {};
     for (let prop in src) {
      let value = src[prop];
       if(value && typeof value === 'object') {
        target[prop] = deepCopy(value);
       } else {
        target[prop] = value;
      }
   }
     return target;
  }
  ,
    getListings: async function () {},
...

Answer 2

When using the spread operator to copy an array, it's important to note that it doesn't create a deep clone. Additionally, if the sort method is used on the original array within a computed property, it can lead to an infinite loop. To avoid this issue, consider adding a method for deep cloning objects like the one mentioned in this reference:

...

 computed: {
    sortedListings: function () {
      return this.deepCopy(this.listings).sort(function (a, b) {
        return b.stick_top - a.stick_top
      })
    },
  },
  methods: {
   deepCopy(src) {
     let target = Array.isArray(src) ? [] : {};
     for (let prop in src) {
      let value = src[prop];
       if(value && typeof value === 'object') {
        target[prop] = deepCopy(value);
       } else {
        target[prop] = value;
      }
   }
     return target;
  }
  ,
    getListings: async function () {},
...

Answer 3

Answer №2

The function getHighlightColor() is causing an infinite loop.

This situation perfectly demonstrates why it can sometimes be problematic (though not always) to bind a method in the template. When a method modifies a model, Vue must re-render the component. This, in turn, triggers the method again, leading to further changes in the model and subsequent re-renders of the component, creating a continuous cycle.

A similar outcome can be achieved through this demo, but not if you utilize computed properties directly in the template:

new Vue({
  el: "#app",
  data() {
    return {
      arr: [1,2,3,4,5]
    }
  },
  methods: {
    change: function () {
      return this.arr.shift();
    },
  },
  computed: {
    test() {
      return this.arr.shift();
    }
  }
});

<div id="app">
  <div>
    {{ change() }}
  </div>
</div>

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

Answer 4

The function getHighlightColor() is causing an infinite loop.

This situation perfectly demonstrates why it can sometimes be problematic (though not always) to bind a method in the template. When a method modifies a model, Vue must re-render the component. This, in turn, triggers the method again, leading to further changes in the model and subsequent re-renders of the component, creating a continuous cycle.

A similar outcome can be achieved through this demo, but not if you utilize computed properties directly in the template:

new Vue({
  el: "#app",
  data() {
    return {
      arr: [1,2,3,4,5]
    }
  },
  methods: {
    change: function () {
      return this.arr.shift();
    },
  },
  computed: {
    test() {
      return this.arr.shift();
    }
  }
});

<div id="app">
  <div>
    {{ change() }}
  </div>
</div>

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

Using the spread operator in a component's render function could potentially lead to an endless update loop

Answer №1

Answer №2

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