Nuxt 3: Pinia: How does changing my state distort the entire array?

Question

This is my code

import { defineStore } from "pinia";

export const DB_CART = defineStore("CART", {
    state: () => ({
        CART: [
            {
                $id: "62616ffc6d13e2a9eb04",
                quantity: 1
            },
            {
                $id: "6261711719aa15827836",
                quantity: 1
            },
            {
                $id: "6275c020740fbd04db50",
                quantity: 1
            }
        ],
    }),
    actions: {
        // INCREMENT PRODUCT QUANTITY IN CART
        incrementCartQuantity(id) {
            const cartItem = this.CART.find(item => item.$id = id);
            cartItem.quantity++;
        },
        // DECREMENT PRODUCT QUANTITY IN CART
        decrementCartQuantity(id) {
            const cartItem = this.CART.find(item => item.$id = id);
            if (cartItem.quantity === 1) return
            cartItem.quantity--;
        },
        // ADD PRODUCT TO CART
        addToCart(item) {
            this.CART.push(item)
        }
    },
    persist: true
})

I want to understand why the array rearranges when I increment or decrement the cart item starting from the second one in the array.

incrementCartQuantity(id) {
   const cartItem = this.CART.find(item => item.$id = id);
   cartItem.quantity++;

   console.log(this.CART) /*EXPECTED OUTPUT
    [
            {
                $id: "62616ffc6d13e2a9eb04",
                quantity: 1
            },
            {
                $id: "6261711719aa15827836",
                quantity: 1
            },
            {
                $id: "6275c020740fbd04db50",
                quantity: 1
            }
        ]
  *//*RETURED OUTPUT
    [
            { $id: "6261711719aa15827836", quantity: 2 },
            { $id: "6261711719aa15827836", quantity: 1 }, INCREMENTED OBJECT
            { $id: "6275c020740fbd04db50", quantity: 1 }
        ]
  */
 },

In my Vue component, on incrementCartItem, I find that the entire array gets shuffled and pops the top array and replaces it with the item that is being mutated I don't think arrays are affected in any way.

Answer 1

Your find method is performing an assignment "=" instead of a comparison "= == ".

replace

  this.CART.find(item => item.$id = id);

and

  this.CART.find(item => item.$id === id);

In both shopping cart methods.

Your find will assign the searched id to the $id of the first item each time it is run.