index.js

const { createSelector } = require('reselect');

const cart = {
    items: [
        { name: 'Item 1', value: 200, in_stock: true },
        { name: 'Item 2', value: 100, in_stock: false },
        { name: 'Item 3', value: 200, in_stock: true },
    ]
}

// Using Reselect
const inStock = createSelector(
    state => state.items,
    items => items.filter(item => item.in_stock)
);

const inStockItems1 = inStock(cart);
const inStockItems2 = inStock(cart);

console.log(inStockItems1 === inStockItems2) // returns true