Troubleshooting a reactivity problem with Nuxt 3/Vue 3 when rendering components within a v-for loop

Question

Troubleshooting a reactivity problem with Nuxt 3/Vue 3 when rendering components within a v-for loop

Hello fellow community members :) I seem to be facing an issue related to reactivity and I could use some advice.

Description

I have a component called FileInput.vue. This component allows me to upload files to my project. Whenever a new image is added, a new field gets pushed to the form.allImages reactive array:

@add="addImageField"

The addImageField function looks like this:

const addImageField = (): void => {
  form.allImages.push({ filename: '' });
};

Here is the reactive data structure:

import type { Images } from '@/types/images.d';

interface Work {
  allImages: Images[];
}

const form: Work = reactive({
  allImages: [{ filename: '' }],
});

Problem description

When I add 2 images and then try to delete the first one using the following function:

const deleteImageField = (index: number): void => {
   form.allImages.splice(index, 1);
};

The first block gets removed correctly and the second one takes its place as expected. However, the second image block should now be empty with a clear value to allow for another image to be added. Although the value of the second element in form.allImages is cleared, the component block still displays the image that belonged to the previous first element in the array.

Check out the image here: https://github.com/nuxt/nuxt/assets/73745478/74981582-05ea-4910-9387-7240dc4394c2

Reproduction

You can see the reproduction by visiting this link: https://stackblitz.com/edit/nuxt-starter-qeaeuf?file=app.vue.

How to use the reproduction

Click on the Add Image block, select any image from your PC, and a static favicon.ico file will be displayed as an example. You will also see a Delete button for deleting the image. Above all the blocks, you can track the data using the {{ form.allImages }}.

Expected behavior

After deleting the image block, it should be completely empty (without displaying any image) and ready for the user to upload a new one.

**I appreciate your attention and any help would be greatly appreciated :) If you have suggestions for improving the code, please feel free to share them as well. Thank you.**

javascript vue.js frontend nuxt.js

Answer 1

Answer №1

To ensure that your key in the v-for is effective, it should be placed on the same element as the v-for. Avoid using the index as the key since it may not provide a unique identifier for each item, especially when elements are being added or removed from an array.

An easy fix is to include a unique id field based on a counter variable that increments every time a new item is added to the array.

interface Images {
  filename: string
  id: number
}

let count = ref(0);
const form: Work = reactive({
  allImages: [{ id: count.value++, filename: '' }],
});

const addImageField = (): void => {
  form.allImages.push({ id: count.value++, filename: '' });
};

Update your v-for loop with:

<div v-for="(image, index) in form.allImages" :key="image.id"

Check out the updated StackBlitz demo

Other issues addressed:

const { text, required, modelValue } = props;

Avoid destructuring props as it can cause reactivity loss. Access props inside the setup() function using props.propName, outside setup as this.propName, or directly in the template as propName. No need to return props from setup, as they are automatically returned.
Rename your custom Button component to avoid conflicts with the HTML reserved <button> element.

Answer 2

To ensure that your key in the v-for is effective, it should be placed on the same element as the v-for. Avoid using the index as the key since it may not provide a unique identifier for each item, especially when elements are being added or removed from an array.

An easy fix is to include a unique id field based on a counter variable that increments every time a new item is added to the array.

interface Images {
  filename: string
  id: number
}

let count = ref(0);
const form: Work = reactive({
  allImages: [{ id: count.value++, filename: '' }],
});

const addImageField = (): void => {
  form.allImages.push({ id: count.value++, filename: '' });
};

Update your v-for loop with:

<div v-for="(image, index) in form.allImages" :key="image.id"

Check out the updated StackBlitz demo

Other issues addressed:

const { text, required, modelValue } = props;

Avoid destructuring props as it can cause reactivity loss. Access props inside the setup() function using props.propName, outside setup as this.propName, or directly in the template as propName. No need to return props from setup, as they are automatically returned.
Rename your custom Button component to avoid conflicts with the HTML reserved <button> element.

Troubleshooting a reactivity problem with Nuxt 3/Vue 3 when rendering components within a v-for loop

Description

Problem description

Reproduction

How to use the reproduction

Expected behavior

Answer №1

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