Libraries like libjpeg solve one non-trivial problem and have been around forever and don't change very quickly. An implementation can be done by hand but it u

Libraries like libjpeg solve one non-trivial problem and have been around forever and don't change very quickly. An implementation can be done by hand but it usually doesn't make sense to do so because the library has been around and stable long enough to be able to presume that it does it in a more performant way and is aware of possible gotchas that it avoids. A database is a large enough project that writing one every time you need one doesn't make any sense. It's probably more work than whatever you are working on. Using one that has been around for a while and that doesn't change quickly makes sense. Grabbing a quick javascript library to do something relatively trivial that is going to bring in megabytes of supporting libraries whose provenance is unknown and that change often is a completely different matter.