There are five simple data types also called primitive data types in java script. Those are Undefined, Null, Boolean, Number, and String. There is also one complex data type called Object.
undefined - if the value is undefined
Eg: var msg;
alert(typeof msg);
boolean - if the value is a Boolean
Eg: var bol = true
alert(typeof bol);
string - if the value is a string
Eg: var str = "some string";
alert(typeof str);
number - if the value is a number
Eg: var no = 123;
alert(typeof no);
object - if the value is an object or null
function - if the value is a function