Lazy ID with memoization

memoized-lazy-id.js

const nullFn = (fn) => typeof fn === 'function' ? fn : () => null;

function dict(key, value, struct) {
    return (function (localStruct) {
        return (ref) => ref === key ? value : localStruct(ref)
    })(nullFn(struct));
}

function memoize(fn) {
    let store = null;

    return function (value) {
        const storedResult = store !== null ? store(value) : null;
        const result = storedResult !== null ? storedResult : fn(value);

        store = storedResult !== null ? store : dict(value, result, store);

        return result;
    }
}

const getUniqueId = (function () {
    let currentId = 0;
    return () => currentId++;
})()

const getId = (function (getId) {
    return function () {
        return getId(this);
    }
})(memoize(getUniqueId));

function setLazyId(obj) {
    return Object.defineProperty(obj, 'id', {
        get: getId
    });
}

const myObj = setLazyId({});