What is the difference between a library and a framework?

The distinction is who's in control. With a library, your code calls it. With a framework, it calls your code. That's the whole thing — often summarised as 'inversion of control'. A library is a toolbox. You write the program, and when you need something specific you reach for a tool: 'format this date', 'make this HTTP request', 'sort this data'. You decide the structure, the flow, and when the library gets used. You can swap it out or use three at once. A framework is a building with rooms already laid out. It defines the structure of your application, and you fill in the parts specific to your app. It decides when your code runs — you provide a function and the framework calls it at the right moment. You fit into its conventions rather than it fitting into yours. Examples that make it clear: a date formatting utility is a library — you call `format(date)` whenever you want. A full web framework like Angular, Django or Rails is a framework — it handles the request lifecycle, routing and structure, and calls your controller or component at the appropriate point. Why React causes arguments: React technically calls itself a library, and strictly speaking it is one — it does one job (rendering UI from state) and doesn't dictate your routing, data fetching or file structure. But it does call your components rather than the reverse, and in practice React-with-its-ecosystem feels framework-shaped. Both descriptions are defensible, which is why the debate never ends. It also does not matter for any practical decision you'll make. The practical trade-off, which is what's actually worth knowing: - Frameworks give you structure, conventions and a lot of decisions made for you. Faster to start, consistent across teams, easier onboarding — at the cost of flexibility, and painful if you need something outside its assumptions. - Libraries give you control and composability, at the cost of having to make (and maintain) architectural decisions yourself. Great for experienced teams, overwhelming for beginners who don't yet know what good structure looks like. If you're early in your learning, mildly prefer the more opinionated option. Having conventions handed to you removes a category of decisions you don't yet have the experience to make well, and you'll learn the reasoning behind those conventions by living inside them.