For a GET request, do I have to specify the null value in the send fucntion or can I just do this:
Second question: in the open() method, can I do this: leaving ou the third argument of true for async requests... the true is the default after all!)
In a larger perspective, can I leave out values that are default values in functions?
To answer your questions:
1. Yes, you may leave out the 'null'
2. Async is 'true' by default, so it is not necessary to include that argument
3. This question is slightly ambiguous. For "built-in" functions/methods, the default values are typically unnecessary. For user-defined functions, you need to programmatically deal with the absence of an argument and define the default value.