Out of curiosity: do you actually use `Function.prototype.toString()`? I haven't seen any use of this method in years. Plus the few uses that I have seen were libraries that attempted to rewrite other libraries and broke at pretty much each update of their dependencies.
There may be legitimate uses of this method in production code, but I can't think of any from the top of my mind. If you can think of one, don't hesitate to file it as an issue in the linked tracker.
Prior to ES2015, the spec's definition of Function.prototype.toString() was pretty vague. The behavior was implementation-dependent, although I don't know the differences per browsers, since I've never used this feature seriously. Here's the text from ES5.1 [0]:
> An implementation-dependent representation of the function is returned. This representation has the syntax of a FunctionDeclaration. Note in particular that the use and placement of white space, line terminators, and semicolons within the representation String is implementation-dependent.
That's... an interesting use. I'm pretty sure it violates the actual specifications of JavaScript, breaks in presence of a minifier/uglifier and slows down your script, but it's a cool hack :)
There may be legitimate uses of this method in production code, but I can't think of any from the top of my mind. If you can think of one, don't hesitate to file it as an issue in the linked tracker.