Javascript Primitive Data Types

It’s important to understand that there are 5 primitive data types in Javascript. Knowing these by heart would be a good idea. The 5 data types are:

  1. Number (All javascript numbers are floating point – meaning a 5 is actually 5.0);
  2. String: Any string of text.
  3. Boolean: True or False.
  4. Undefined: The default state of a variable before a value is assigned to it.
  5. Null: Equivalent of nothing.

Examples of other data types which are not classified as ‘primitive’ data types would be objects or arrays


Javascript has dynamic typing, meaning a variable can be any type. In Java for example, a variable equal to “ConquerJS” would be a string.


String blogName = "ConquerJS";

If I changed my blog’s name to a number I loved for some reason, like 3456729, in Java, I could not change ‘blogName’ to that number. I would have to create a new “int” variable to hold my new blog name (Of course I could always make the new numeric blogName a string by wrapping it in quotes).


in Javascript, variable types are processed dynamically, so I can do the following:

var blogName = "ConquerJS";

blogName = 15; <---- This works, my variable now holds a number.


I can concatenate different data types and javascript will convert those types to one type. For example ,  if you have

var name = "rup";

var age = 50;

var handsome = false;

I can add them together like

console.log(name + age + handsome);

This will evaluate to a string, since you can’t turn a string into a number most of the time because words are not numbers, but numbers can always be strings, as can Booleans.