Comment by beaconstudios

    const leftpad = (str, len, char = ' ') => str.length >= len ? str : (char.repeat(len - str.length) + str);

Anybody who installs a dependency instead of writing a one line function is just leaving themselves exposed for no real benefit.

Providing the at function outside of the prototype chain like I did above will not incur the cost you mentioned, even in the unlikely case that such calls are the bottleneck of your application.

Plus, if array lookup calls are your bottleneck then you probably need a different data structure.