Performance issues with infinite scrolling and v-for - vue.js

Question

I’ve just recently started using Vue and so far so good, but I’ve ran into a bit of an issue that I can’t figure out a good solution to.
I have a photo gallery with a few different sections. I have an overall gallery component, a gallery section component and an image component. Essentially, I’m using a photos array for each section to store the photos data for that section. Within the sections I’m using v-for to display the photos. The gallery is infinitely scrolling so when you scroll to the bottom, more images load and the photos array for that section is updated.
Here’s my problem, currently the photos arrays are stored on the data of the overall gallery component, so when I update one of the photos arrays it seems to cause the entire gallery to rerender. The more images on the screen, the worse effect this has on the performance and the less responsive the page becomes.
I’m aware I could move the photos array to the data of the individual sections, but as far as I can tell this would still rerender that entire section.
I don’t really know if there’s any good solution that’ll do what I’m trying to do, having a certain amount of reactivity but only updating the things that changed. I don’t know if something like that is possible.
I’ve tried messing around with computed data, props, methods etc. but I can’t work out a better solution.
Here’s the code I’ve been working with in the overall gallery component:
<template>
<div class="photo-gallery">
<gallery-section v-for="(section, index) in sections" v-bind:section="section" class="photo-gallery__section" v-bind:key="index"></gallery-section>
</div>
</template>
<script>
import * as qb from "../queryBuilder";
let layout = [
{
title: "Highlighted Photos",
request: {
filters: qb.group([
qb.filter("rating", ">=", 4),
]),
options: {
offset: 0,
limit: 2,
order: ["rand()"],
size: 740
}
},
total: 2,
photoClass: "photo--highlighted",
loading: false,
photos: []
},
{
title: "More photos",
request: {
filters: qb.group([
qb.filter("rating", ">=", 2),
]),
options: {
offset: 0,
limit: 40,
order: ["rand()"]
}
},
total: Infinity,
loading: false,
photos: []
}
];
export default {
data() {
return {
sections: layout,
currentSection: 0
}
},
mounted() {
this.getPhotos(this.sections[0]);
this.getPhotos(this.sections[1]);
},
methods: {
getPhotos(section) {
section.loading = true;
let currentSection = this.currentSection;
fetch(`api/photos/search/filter/${JSON.stringify(section.request.filters)}/${JSON.stringify(section.request.options)}`)
.then(response => response.json())
.then(response => {
section.photos.push(...response.images);
// Set offset for next request
this.sections[this.currentSection].request.options.offset = section.photos.length;
// Check if current section is complete or if less than the requested amount of photos was returned
if (
this.sections[this.currentSection].total === section.photos.length ||
response.images.length < this.sections[this.currentSection].request.options.limit
) {
if (this.sections.length -1 != this.currentSection) {
// Move onto next section
this.currentSection++;
} else {
// Set currentSection to null if all sections have been fully loaded
this.currentSection = null;
}
}
})
.finally(() => {
section.loading = false;
});
},
scrollHandler() {
if ((window.innerHeight + window.scrollY) >= document.body.offsetHeight - 500) {
if (this.currentSection != null && !this.sections[this.currentSection].loading) {
this.getPhotos(this.sections[this.currentSection]);
}
}
}
},
created() {
window.addEventListener("scroll", this.scrollHandler);
},
destroyed() {
window.removeEventListener("scroll", this.scrollHandler);
}
}
</script>
One thing I've also noticed is that whenever more photos are loaded, the mount function for every photo component on the page runs.
Would anyone be able to point me in the right direction? Any advise would be very much appreciated.
Thank you, Jason.

Answer 1

The issue was the the way I was generating the keys for my photos component instances, which cannot be seen in the code I included above. I figured out that the random number being generated as the key meant Vue could not keep track of the element as the key would keep changing. I'm now generating unique keys on the server side and using them instead. It works as expected now.