JavaScript undefined Property

Below is the example of the undefined Property.

• Example:
  
  

  
  
  

  <script>     var a ="Geeksforgeeks"     function test() {         if (typeof a === "undefined") {             txt = "'a' is undefined";         } else {             txt = "'a' is defined";         }         document.write(txt);     }     test(); </script>

• Output:

  'a' is defined

The undefined property is used to check if a value is assigned to a variable or not.

Syntax:

var x;
if (typeof x === "undefined") {
  txt = "x is undefined";
} else {
  txt = "x is defined";
}

Return Value: It returns ‘defined’ if the variable is assigned any value and ‘undefined’ if the variable is not assigned any value.

More example code for the above property are as follows:
Program 1:

Output:

Supported Browsers:

• Google Chrome
• Firefox
• Internet Explorer
• Opera
• Safari