array.prototype.at
An ES-spec-compliant (proposed) Array.prototype.at shim/polyfill/replacement that works as far down as ES3
hasharray
A data structure that combines a hash and an array for fast dictionary lookup and traversal by complex keys.
slick-array
Native JavaScript Array, but extended with custom indexing and group support for super-fast lookups.
p-locate
Get the first fulfilled promise that satisfies the provided testing function