CappyJuices

function solve(input) {

    let bottles = new Map();
    let juiceStorage = {};

    input.forEach(juice => {
        let [type, quantity] = juice.split(' => ');
        quantity = Number(quantity);

        if (!juiceStorage[type]) {

            juiceStorage[type] = quantity;

        } else {

            juiceStorage[type] += quantity;

        }
        if (juiceStorage[type] >= 1000) {

            if (!bottles.has(type)) {

                bottles.set(type, []);
                bottles.get(type).push(quantity);

            } else {

                bottles.get(type).push(quantity);

            }
        }
    });
    Array.from(bottles).forEach(el => {
        let quantity = parseInt((el[1].reduce((a, b) => a + b, 0)) / 1000);
        console.log(`${el[0]} => ${quantity}`);
    });

}
solve(['Kiwi => 234',
    'Pear => 2345',
    'Watermelon => 3456',
    'Kiwi => 4567',
    'Pear => 5678',
    'Watermelon => 6789'
])