null & undefined

What is Data Type & Variables?

null & undefined

Null type has only one value, null. The null value means 'no data' or this variable do not have any useful data.

Undefined type has one value, undefined, undefined means nothing is stored in this variable. Undefined is not even null.

Initializing null type variable

var food = null

var is JavaScript keyword, food is a variable name, null is value assigned to food variable.

In the example given below we have used keyword document.write (message ) which is used to print the message or variable value given with it.

Example 1

<html>

<head>

</head>

<body>

var food=null

document.write("food is : "+food);

</script >

</body>

</html>

Understanding the program

food is a variable of null type having no type of values or data.

output of this program

food is : null

Knowing undefined type variable

var food ;

var is JavaScript keyword, food is a variable name, no value is assigned to variable food.

In the example given below we have used keyword document.write (message ) which is used to print the message or variable value given with it.

Example 2

<html>

<head>

</head>

<body>

var food;

document.write("food is : "+food);

</script >

</body>

</html>

Understanding the program

food is a variable of undefined type , because nothing is defined to it .

Output of this program

food is : undefined