“types are just arbitrary labels the language doesn’t even know about” is ok if you're aware of the limitations. I add typedefs and other jsdocs to javascript just because it makes it easier to work with in an IDE. it's nice to hover over a variable and see what it's "supposed" to be (if all went well this object should have a .id, might have a .name, etc), sometimes even declared as two types like "this variable is either an int or a boolean". I don't really want to bother learning typescript or trying to get coworkers to do so/put it in the pipeline so it's the best I can do and it certainly makes life a bit easier.