The name of the game is failure aversion. Frameworks and NPM packages for everything. When I interview JavaScript or UI developers this is my first discriminator. Why write original code or reinvent the wheel when somebody else has your simple solution behind 50mb of external code that you didn't write? If you are that fearful coward who believes in not writing original code I don't want to work with you. Have a nice life and go work somewhere else. I would rather work with somebody willing to take a chance on problem solving.
If you are going to down vote please mention why. Don't be a troll. Hacker News tries very hard to not be an echo chamber.
And what's funny is that if you hadn't been a jerk the original point of Frameworks and NPM Packages for everything is a good point and probably would have been well received. Because, the fact is that, sometimes it IS better to do it yourself instead of using the package and most wouldn't. Sometimes.
On the other hand, if the existing libraries/solutions don't fit your use cases and you spend more time customizing them to work than you do developing your product, or the existing solutions are out of date, unsupported, or appear slapped together, it would certainly be worth working on your own solution to see if you can find a better way. Likewise, experimenting with custom reimplementation is a great way to understand the problems libraries solve in an in-depth way, as Dan suggests, and you may even end up with something better. You just need to be realistic about whether it makes sense to make it yourself or utilize what exists.