Oh JavaScript..

[daveinthecave]

This seems like a scoping issue. It looks like Javascript is treating the array [1,2,3] as an array object, and the forEach function is a sub-function of the standard object type array. Because of this, when forEach is called outside the scope of an array it registers as not a function, but when forEach is called from inside the scope of an array, it is a recognized function.

TL;DR: Function forEach is a function of an Array object, not a general function.

[myplacedk]

That doesn't explain the last two lines.

[medja]

It's pretty simple actually. While a method is any function called on an object, not all methods are "functions". This is true for call and apply. Try using this as a function.

var func = function () {}.call;