The library is ramdajs.com and it can be grabbed from npm.<p>I do not agree that everything should be handled with standard libraries. It&#x27;s better for these things to be modular and versioned, instead of them being pulled from a big bloated standard library.<p>The code clearly does what was being asked in a very simple and non-broken way.<p>Perhaps the issue here is that non-JavaScript engineers are used to kitchensink standard libraries and avoid mixing and matching to get the best experience the ecosystem offers.