How is this day 4? Didn't we do this in day 1? At least use Symbols if we are learning ES6 features.

The primitive type names provided in the description can be confusing - in fact the primitive types are written in lowercase (opposite to object equivalents which start with the capital letter).

You can try the following to see the real type names:

typeof "16"

typeof 16

typeof true

Doubt Regarding string..!!

var my_str = "Hello World!"; Test case Passed

var my_str = new String("Hello World!"); Test Case not passing

Well they did say "assign" them a particular datatype.

var my_num = "4.2.3".split('.').length;
var my_bool = ((4 + 17) < (25 - 6));
var my_str = (4 + 8 * 3).toString();

I started a GIT branch for those who need a little help let me know if you need explanations added as well https://github.com/giannioudis/7-Days-of-JavaScript