One of the basic tenets of programs is that they have to work on data. Data is any type of information with which you are working. Data can be words, such as "Hello There", or numbers, such as 42 or 381.33. In any case, different programming languages enable you to work on different kinds of data. JavaScript has five fundamental data types: String, Number, Boolean, Object and Null.

	Strings
	Numbers
	Boolean
	Null

A string is any grouping of characters that is surrounded by either double quotation marks (") or single quotation marks ('). Strings are used anytime you want to use text in a program. Single quotes are used when you want to use double quotes in the string.

Example :

"Welcome"
'Good Morning'

'A string that contains "double quotes"'

JavaScript is quite flexible in the ways it enables you to represent numbers. Many programming languages make you divide ahead of time what type of number you will be using.

Example :

18          // The decimal integer 18
104.2     // The floating point number 104.2
0.058     // The floating point number 0.058

A Boolean is the simplest data type available. A Boolean value has only two possible values-true and false. They are often used to represent whether something has been done or not.

Example :

static boolean ans; // ans is a boolean variable
static String first="were";
static String second="where";
if (first= =second) // Checks if string "first" is equal to string "second"
{
            ans=true;
}
else
{
            ans=false;
}

class first
{
String s;// s is a string
public static void main(String args[ ])
   {
               first my = new first(); // Creates an instance of class first
               System.out.println(my.s); //Prints null since String is initialized to null by default
   }
}