JS Reduce Example

reduceExample.js

const starting = [
    {
        potentialUpgrades: ["D-a","D-b","D-c"],
        productName: "D",
        registeredUser: "test4.example.com"
    },
    {
        potentialUpgrades: ["E-a","E-b","E-c"],
        productName: "E",
        registeredUser: "test4.example.com"
    },
    {
        potentialUpgrades: ["101-1","101-2","101-3"],
        productName: "101",
        registeredUser: "test5.example.com"
    }
];

console.log("starting=" + JSON.stringify(starting));

const ending = starting.reduce((acc, obj) => {
    const item = acc.find( itm => itm.registeredUser == obj.registeredUser );
    if( !item ){
        acc.push({
            registeredUser: obj.registeredUser,
            products: [ 
                {
                    productName: obj.productName,
                    potentialUpgrades: obj.potentialUpgrades
                    }]
        });
    } else {
        item.products.push( {
            productName: obj.productName,
            potentialUpgrades: obj.potentialUpgrades
        })
    }
    return acc;
}, [])


console.log("ending=" + JSON.stringify(ending));