What is meant by "JavaScript numbers are always stored as double precision floating point numbers"?

Question

Does this mean:
var num = 12;
creates the variable num and stores it's value as 12.00 as opposed to 12, which is the value I assigned it to? Can someone also explain why Javascript stores values as double precision floating point numbers?

Answer 1

why:
Length of int data types is too short to stored and calculate
Also try to find power of integer that raised by integer without using loop or recursion is pretty hard
but When there is floating point pretty easy to find now