JSFiddle - React, Tailwind, and code Playground

JavaScript

var items = {
    item1: 100,
    item2: 0,
    item3: 0
};

function distribuir(el, qtd) {

    var somaTotal = 0,
        nrItems = 0;
    for (var este in items) {
        if (items[el] != items[este]) {
            somaTotal += items[este];
            nrItems++;
        }

    }

    for (var este in items) {
        if (items[el] != items[este]) {
            if (somaTotal == 0) items[este] += qtd / nrItems;
            else items[este] += (items[este] || 1) * qtd / somaTotal;
        } else items[este] -= qtd;
    }
    console.log(items);
}
distribuir('item1', 10);