[true_religion]

True, but Javascript libraries tend to be pretty small and deal with well-known concepts. Many experienced dev's have seen a router 10x by the time they've come to React-Router, and the entirety of the source code can be read in a single day.

If you both (a) have experience and (b) have read and understood the entirety of a library, then you are in the best position to claim that you can do it better in house.

The prevelance of libraries doing the same thing in Javascript shows that alot of people have different ideas, and due to culture decide to open source it instead of keeping it in-house.

Other communities do the reverse. There are probably a million homebaked Java frameworks that will never see the light of day because people in Java land don't think that MVC is so extra ordinary that they need to release their in-house needs specialized framework.

[douche]

One of the weaknesses of Javascript is its absolutely terrible standard library. In comparison to languages with solid, comprehensive, "batteries-included" standard libraries, you spend a lot of time re-implementing basic functionality. Or you import jQuery, or LoDash, or underscore, or use pieces of Ember or Angular, or React, etc, etc. Or some bastard abomination of all of those.

[bcherny]

I'd argue that's a strength. Note how scala is modularizing its standard lib in Dotty, and TypeScript is doing that same for stdlib typings.

Standard libs are great, but they need to be modular. If they're modular then they are versioned separately from the language, and at that point there's no difference between a well specified and maintained lib (eg lodash) and a stdlib.