Generic memoize function supporting multiple parameter key lookups

memoize_multi.js

function memoize(factory, ctx, mapper) {
    const cache = new Map();
    return function(...keys) {
        const key = mapper ? mapper(keys) : keys[0];
        if (!cache.has(key)) {
            cache.set(key, factory.apply(ctx, keys));
        }
        console.debug(cache);
        return cache.get(key);
    }
}

example usage:

const multiply = memoize((a, b) => a * b, undefined, JSON.stringify);