That's kind of exactly what the second half of my comment was about - if you have static typing, then this problem just doesn't exist. If not, then the problem

That's kind of exactly what the second half of my comment was about - if you have static typing, then this problem just doesn't exist. If not, then the problem is really no different from not knowing what your functions are returning (are they returing a Promise object? are they returning the data itself?). Not knowing the return type of the functions you use is hardly something new. You would have the exact same issue with functions that take callbacks. See the link I sent there https://goo.gl/vDk3Gz https://goo.gl/vDk3Gz - you can hover over all the variables and functions (once the editor fully loads), try typing "n.", hover over the highlighted errors, etc. The tooling takes care of everything.