aggregate array of objects based on certain properties typescript

There's probably a more elegant way, but you could use a string template to represent the product/color combination.

Playground Link

interface Order {
    orderId: number;        
    productName: string;
    color: string;
    quantity: number;
    price: number;
    link: string;
}

interface Summary {
    productName: string;
    color: string;
    quantity: number;
    price: number;
}

const makeKey = (order: Order) => {
    return `${order.productName}_${order.color}`;
}

type AggregatedOrders = {
  [key: string]: Summary;
};
  
const orders: Order[] = [
    {
        color: "blue",
        link: "https://savantly.net",
        orderId: 123,
        price: 999,
        productName: "hello",
        quantity: 1
    },
    {
        color: "green",
        link: "https://savantly.net",
        orderId: 345,
        price: 999,
        productName: "hello",
        quantity: 1
    },
    {
        color: "green",
        link: "https://savantly.net",
        orderId: 234,
        price: 999,
        productName: "hello",
        quantity: 1
    }
];

const groups: AggregatedOrders = {};
orders.forEach(o => {
    const key = makeKey(o);
    if(!groups[key]) {
        groups[key] = o;
    } else {
        groups[key].price += o.price;
        groups[key].quantity + o.quantity
    }
});
// grouped by product and color
console.log(groups);