(edited after 2m, added the first paragraph) You gave an example the OS theory would only be good when writing an OS. But the (valid) counter point was that it

(edited after 2m, added the first paragraph) You gave an example the OS theory would only be good when writing an OS. But the (valid) counter point was that it also becomes relevant when interfacing with an OS. JavaScript first and foremost runs on your browser, not on the OS itself. So understanding how browsers work (DOM, APIs, XHR...) becomes akin to understanding how the OS works. (I also have the following rant, which I don't like too much [too polemic] after posting, but I'm keeping it for transparency sake) No-one claimed you need to know quantum physics to understand what happens to the electrons in your CPU; but generally it's a good idea to know how the next few layers you're interfacing with work (in either direction). And that's often the OS, or the network, or the cache behaviour of your CPU or the superscalar nature of the GPGPU you use to accelerate something important. Or another something attached by some bus to your MCU in the embedded device you're building, or maybe the user navigating that website.