Javascript mapping array with an object

Question

I have a question about the Javascript mapping array with an object.

cart.json:

{ "products": [ { "id": "0.17912240212736852","qty": 1 } ], "totalPrice": 336 }

Here is my code:

let cart = { products: [], totalPrice: 0 };

const a = cart.products.map(product => {
    product.id === id ? { ...product, qty: product.qty + 1 } : product;
});

// Undefined
console.log(a);

The Result I want is to add 1 to the qty

Even if I tried to do the following:

const a = cart.products.map(product => {
    console.log(product);
});

// Undefined
console.log(a);

Can any explain what is the problem? Thank you.

your arrow function isn't return anything. Use return to return the expression, or remove the function body {} to implicitly return. — Nick Parsons
– Nick Parsons, Commented May 22, 2020 at 9:21
A .forEach() with a simple += 1 would be easier (unless you really need a copy of cart.products) — Andreas
– Andreas, Commented May 22, 2020 at 9:22
Thanks! I always forget to return when I do mapping....... I will try forEach() as well! — Peter Wu
– Peter Wu, Commented May 22, 2020 at 9:27

Daniel Herrero Hernando · Accepted Answer · 2020-05-22 09:21:22Z

2

You are not returning anything, try wrapping the {} with () or directly write return,

Like this:

let cart = { products: [], totalPrice: 0 };

const a = cart.products.map(product => {
    return product.id === id ? { ...product, qty: product.qty + 1 } : product;
});

// Undefined
console.log(a);

answered May 22, 2020 at 9:21

Daniel Herrero Hernando

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