Data Structure
Networking
RDBMS
Operating System
Java
MS Excel
iOS
HTML
CSS
Android
Python
C Programming
C++
C#
MongoDB
MySQL
Javascript
PHP
Physics
Chemistry
Biology
Mathematics
English
Economics
Psychology
Social Studies
Fashion Studies
Legal Studies
- Selected Reading
- UPSC IAS Exams Notes
- Developer's Best Practices
- Questions and Answers
- Effective Resume Writing
- HR Interview Questions
- Computer Glossary
- Who is Who
What is the difference between JavaScript undefined and void(0)?
JavaScript undefined
It means a variable declared, but no value has been assigned a value.
For example,
var demo; alert(demo); //shows undefined alert(type of demo); //shows undefined
Here’s another example showing the usage of undefined to check whether a variable exists or not:
Example
<html>
<body>
<script>
var age = 10;
if( typeof age !== 'undefined' ) {
document.write("True");
} else{
document.write("False");
}
</script>
</body>
</html>Output
True
JavaScript void(0)
The void is an important keyword in JavaScript, which can be used as a unary operator that appears before its single operand, which may be of any type. This operator specifies an expression to be evaluated without returning a value.
The syntax of the void can be either of the following two −
<head> <script> <!-- void func() javascript:void func() or: void(func()) javascript:void(func()) //--> </script> </head>
Updated on: 16-Jun-2020
341 Views
Advertisements