Typescript adding property to inline interface

Question

i Would like to know if there is a way to add parameters to a interface of an already created object... Let me explain

I have a Product Class with these properties product.id product.name, now i want to add a quantity property to it... I´m making an sql query that will give me the product object and the quantity and I want to add it to the product interface only to this const so I can do something like console.log(products[0].quantity)

I was tring to do something like this but obviously doesn't work

const products:Array<{...Product, quantity: number}> = (some sql query code with joins xd)

I found a way and is declaring all from scracth but I want to know if there is a better way to do this because this is a little cumbersome specially if the object has more properties

const products:Array<{id: number, name: string, quantity:number}>

Edit: Just found a way but I'm still all ears

const products:Array<Product & {quantity: number}>

Assuming you can’t modify the original Product type, your method of intersection types is usually what I’d defer to. You could also make a type alias for it if you need it in multiple places. — y2bd
– y2bd, Commented Mar 10, 2021 at 0:14

fippi · Accepted Answer · 2021-03-10 00:14:46Z

1

Intersection Types

I'm assuming you already have a Product interface i.e.

interface Product {
    foo: string;
    bar: number;
}

You would do it like so

const products = Array<Product & { quantity: number }> = await db.getFromDBExample();

// Example response
console.log(products); // { foo: 'hello', bar: 2, quantity: 3 }

answered Mar 10, 2021 at 0:14

fippi

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