Depends partly on how you learn, generally a better approach to learning a programming language (from my perspective) would be to work on a project or some problems that way you will have runnable code in that language that you can reference back to at any point. If you do take programming notes it is also useful to capture edge cases or syntax comparisons either against two languages or different approaches you can take in a single language rather than just noting down syntax.
But more recently if I just want to refresh my knowledge on the syntax of a language I use: https://learnxinyminutes.com which has syntax cheatsheets for a lot of languages