Difference between creating new instance by constructor and without constructor in javascript

Question

Formed an object 'myclass' in my js file like this:

var myclass = function(){
  this.m1 = function(){
    return "THis is m1 of myclass"
  };
  return "this is myclass";
}
myclass.prototype.mp1 = function(){
   return "this is mp1 of myclass"
}

now i do this:

var a = new myclass();
var b = new myclass;

Q1- I dont see any difference between the behaviors of these two. Please explain the reason.

Q2 - When I do - console.log(a), i expect to get "this is myclass" in console, but instead I see [object object].

Q3 - If I return an object from the constructor of 'myclass'(eg - return {x:1}), then I cannot use 'm1' or 'mp1' anymore from the instances of 'myclass'.

Q4 - Comparing this with Date class of window object, this is totally different behavior. If a = new Date(), then i see value of 'a' as a date although the type is an object, and this points to my next question.

Q5 - The date class returns a date which looks like a string in DOM but the 'typeof' of the instance of date class is an object. Why's that?

Sorry for posting so many questions at once, but it would be nice if I get answers for all questions as I think they are related.

This question is not about a particular question from the above 5. But combination of all. As I have to know the return type, comparison between myclass() and myclass, and comparison between myclass() and Date()/predefined window objects.

Answer 1

First of all, i will advice you to read Introduction_to_Object-Oriented_JavaScript.
You will find a lot of answers.

Quickly :

Q1- I dont see any difference between the behaviors of these two. Please explain the reason.

it is true in your use case, because your constructor don't need arguments.

Q2 - When I do - console.log(a), i expect to get "this is myclass" in console, but instead I see [object object].

this is because you try to log the Object not the result of a function.
you shoul do : console.log( a.m1() );

Q3 - If I return an object from the constructor of 'myclass'(eg - return {x:1}), then I cannot use 'm1' or 'mp1' anymore from the instances of 'myclass'.

simply : why would you do that ? returning something else than an instance for a constructor ?

Q4 - Comparing this with Date class of window object, this is totally different behavior. If a = new Date(), then i see value of 'a' as a date although the type is an object, and this points to my next question.

in reality there is an built-in function toString for every object and it is called when you try to "convert/to print" an object to string.

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edit

from the comment of Ward D.S.
the default toString of anything simply returns the type. usually object Object. If you want this behaviour changed, simply overwrite the .prototype.toString of your class and return what you want

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when you call : console.log(myDate);
the underground is console.log( myDate.toString() )
this is why you see your date string.

If you want the same behaviour you have to add :

var MyClass = function(){
  this.name = 'i am a MyClass';
}
MyClass.prototype.toString= function(){ return this.name };

var a = new MyClass();
document.write (a)

Q5 - The date class returns a date which looks like a string in DOM but the 'typeof' of the instance of date class is an object. Why's that?

because everything in javascript is an Object