Data Types - Null and Undefined

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Null

• Null is a special value indicating that they variable has no value what so ever.
• Null is not equal to 0 nor "" (the empty string)

Undefined

• A variable with the data type of undefined is a variable that has been declared, but never given a value.
• Variable with undefined values can not be used in calculations.

Try the following program out.

var x;
var y = null;
var z = "";

document.write("x= " + x + "<P>");
document.write("y= " + y + "<P>");
document.write("z= " + z + "<P>");

if (y==z) document.write("y = z<P>");

Run the above program.

Try adding the statement

if (x == y) document.write("x = y<P>");

Run with the modification.

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