[Nexus]

const push = (function() {
    const container = [];
    const alreadyInContainerIndex = {};

    const checkItem = function(item) {
        return item === null || !alreadyInContainerIndex[item.id];
    };

    return function(data) {
        if (!checkItem(data))
            return;

        const index = container.push(data) - 1;
        if (data)
            alreadyInContainerIndex[data.id] = index;
    }
})();