The term framework itself is kind of hard to define and in many cases almost identical to "library". Is express.js a library or already framework? Or both? At least it calls itself a framework..

Many libraries or frameworks do one thing and one thing well, but there are also frameworks that are a collection of libraries for different purposes. I feel entrenched when frameworks limit library choice by making it hard to switch out components. From that perspective I prefer libraries over frameworks, but the distinction is kind of hard to make.