Setting/resetting Vue reactive objects

Vue 3 has many idiosyncrasies, among them the overlapping ref and reactive constructs. One of the main differences is that reactive content cannot be replaced. One StackOverflow answer proposes using Object.assign, but it will replace all nested references, losing them all.

I ended up writing my own version of a recursive function to replace each value inside an object, so I won’t need to deal with the muddy details ever again:

/**
 * Recursively copies each field from src to dest, avoiding the loss of
 * reactivity. Used to copy values from an ordinary object to a reactive object.
 */
export function deepAssign<T extends object>(destObj: T, srcObj: T): void {
	const dest = destObj;
	const src = toRaw(srcObj);
	if (src instanceof Date) {
		throw new Error('[deepAssign] Dates must be copied manually.');
	} else if (Array.isArray(src)) {
		for (let i = 0; i < src.length; ++i) {
			if (src[i] === null) {
				(dest as any)[i] = null;
			} else if (src[i] instanceof Date) {
				(dest as any)[i] = new Date(src[i].getTime());
			} else if (Array.isArray(src[i])
					|| typeof src[i] === 'object') {
				deepAssign((dest as any)[i], src[i]);
			} else {
				(dest as any)[i] = toRaw(src[i]);
			}
		}
	} else if (typeof src === 'object') {
		for (const k in src) {
			if (src[k] === null) {
				(dest as any)[k] = null;
			} else if (src[k] instanceof Date) {
				(dest[k] as any) = new Date((src[k] as any).getTime());
			} else if (Array.isArray(src[k])
					|| typeof src[k] === 'object') {
				deepAssign(dest[k] as any, src[k] as any);
			} else {
				(dest[k] as any) = toRaw(src[k]);
			}
		}
	} else {
		throw new Error('[deepAssign] Unknown type: ' + (typeof src));
	}
}

Another problem with reactive is that, to avoid two variables pointing to the same point, we must deep clone an object when creating the object. I also wrote a function to deal with that:

/**
 * Deeply clones an object, eliminating common references. Used to create a
 * reactive object by copying from an ordinary object.
 */
export function deepClone<T>(origObj: T): T {
	const obj = toRaw(origObj);
	if (obj === undefined
			|| obj === null
			|| typeof obj === 'string'
			|| typeof obj === 'number'
			|| typeof obj === 'boolean') {
		return obj;
	} else if (Array.isArray(obj)) {
		return obj.reduce((acum, item) => [...acum, deepClone(item)], []);
	} else if (obj instanceof Date) {
		return new Date(obj.getTime()) as unknown as T;
	} else if (typeof obj === 'object') {
		return Object.entries(obj).reduce(
			(acum, [key, val]) => ({...acum, [key]: deepClone(val)}), {}) as T;
	} else {
		throw new Error('[deepClone] Tipo desconhecido: ' + (typeof obj));
	}
}

I remember from my MobX days some people saying that working with reactive variables can be tricky. Now I can clearly see why.

Checking if user passed a slot in Vue

In Vue 3 with the Composition API, there is no this.$slot entry to programmatically poke on the slots. You must summon the slots by calling useSlots() – yes, that’s a React hook right there.

The returned object has one entry for each slot. If your component has only one unnamed slot, it will be named 'default'. So, in order to check whether the user didn’t pass the slot, you simply check whether the entry exists:

<script setup lang="ts">
import {computed, useSlots} from 'vue';

const slots = useSlots();
const hasSlot = computed(() => slots['default'] !== undefined);
</script>

Filtering Pinia store fields

I’m having great joy working with Pinia, so much I’m introducing it at work. It seems reliable so far.

I found a quirk that’s annoying, however. In VS Code autocomplete, all the contents of the store are exposed – that includes all the internals we should not see.

After digging into the code and a lot of experimentation, I finally found a way to filter the visible fields using TypeScript:

import {defineStore, StoreActions, StoreGetters, StoreState} from 'pinia';
	
const useDef = defineStore('main', () => {
	return {};
});

export type ReachableStore =
	StoreActions<ReturnType<typeof useDef>> &
	StoreGetters<ReturnType<typeof useDef>> &
	StoreState<ReturnType<typeof useDef>>;
const useStore = (): ReachableStore => useDef();
export default useStore;

Although those types are exported by Pinia, they have basically zero documentation. I’m considering contribute with some documentation improvement, but I’m unsure if it’s worth.

Loading data asynchronously with Vue and Pinia

When working with Vue 3 Composition API and Pinia, I struggled a bit to put out an example of loading async data, where the request is handled by the Pinia store, which also owns the data.

It’s 2 AM and, finally, here is the store:

import {ref, reactive} from 'vue';
import {defineStore} from 'pinia';

const useStore = defineStore('fruits', () => {
	const fruits = reactive<string[]>([]);
	const loading = ref(false);

	return {
		fruits,
		loading,
		loadFruits(): Promise<void> {
			loading.value = true;
			return new Promise((resolve, _reject) => {
				setTimeout(() => {
					fruits.push('lemon', 'orange', 'peach', 'strawberry');
					loading.value = false;
					resolve();
				}, 2000);
			});
		},
	};
});

export default useStore;

And this is the single file component, which calls the store asynchronously:

<template>
	<div v-if="loading">Loading...<div>
	<div v-if="!loading">
		<div v-for="fruit of fruits" :key="fruit">
			{{fruit}}
		</div>
	</div>
</template>

<script setup lang="ts">
import {computed, onMounted} from 'vue';
import useStore from '@/model/store';

const store = useStore();
const loading = computed(() => store.loading);
const fruits = computed(() => store.fruits);

onMounted(() => {
	store.loadFruits();
});
</script>

Although I’m not seeing much advantage of Vue over React, Pinia is so much better than Redux insanity. Even with Redux Toolkit. I hope they don’t mess it up when Pinia becomes Vuex 5, as said.

Vue.js builds for non-root web directories

The React’s lack of scoped CSS annoyance made me want to try Vue.js, which solves this problem right out of the box. And so far, I’m liking this framework quite a lot, I must admit. The idea of single file components pleases me greatly.

This morning I stomped over a problem: I was generating a build release to run under a non-root directory in my web server, and the application was getting lost by searching the files at the server root.

Fortunately I’m using vue-cli v3, actually 3.0.0-rc.3, which has quick solution, as I found here.