Function Invocation and `this`

functions

1. When a function is invoked by '()' , `this` is set to the window global object.
2. Invocation as a method of an object will set `this` to the object itself. 
3. Invocation as a contstructor referenced with the 'new' keyword, the object is passed as 'this' to the constructor and any absence of an explicit return value with always return the new object created as the constructor.
4. Invocation via call/apply passes an object as function parameter & that object will be set to `this`.