This is an open-source project, where we try to do a polyfill for every (or almost all of them) Javascript Methods that currently exist. You can use them as polyfills for your project, to learn how to replicate a specific method, or any purpose you would need.
A polyfill is a recreation of an existing resource, that can be used if a browser or context doesn't have support for the original one. For example, if you enter Mozilla Array.prototype.flat() compatibility you will see that it doesn't exist on Internet Explorer, so a way to keep using it would be inserting a polyfill that recreates that method using supported methods.
First download/clone/fork the repo, now go to the terminal and type npm run time <object/method>, for example npm run time array/flat or npm run time array/map.
That script will run their test, which you can locate at the folder "test/object/method.js", you can change the test however you like.
Fell free to add an issue if you find any bug, or maybe a pull request for any improvement you think would be useful :).
*New polyfills are accepted, but you can also modify the ones that are already there.