Function context (“this”) in nested functions

Question

When you invoke a top-level function in Javascript, the this keyword inside the function refers to the default object (window if in a browser). My understanding is that

Answer 1

Whether a function is nested inside another one has nothing to do with the value of this when the function is called. The only things that matter are:

• If the function is "found" by traversing a property on an object, then the value of this will be a reference to that object:

  someObject.prop( whatever );
  

  It doesn't matter how the function was declared.

• If you use call() or apply() to invoke a function, then the value of this is taken from the first argument to whichever of those functions you use.

• If you've created a bound wrapper for the function with bind(), then the value of this will be as requested when bind() was called.

• If you're calling a function as a constructor with new, then this will refer to the newly-created object instance.

• Otherwise, this is either a reference to the global context, or else it's undefined (in "strict" mode or in an ES5-compliant runtime).

The "location" in the code where a function is defined does matter, of course, in that the scope includes whatever symbols it includes, and those are available to the function regardless of how a reference to it is obtained.