- Javascript Basics Tutorial
- Javascript - Home
- Javascript - Overview
- Javascript - Syntax
- Javascript - Enabling
- Javascript - Placement
- Javascript - Variables
- Javascript - Operators
- Javascript - If...Else
- Javascript - Switch Case
- Javascript - While Loop
- Javascript - For Loop
- Javascript - For...in
- Javascript - Loop Control
- Javascript - Functions
- Javascript - Events
- Javascript - Cookies
- Javascript - Page Redirect
- Javascript - Dialog Boxes
- Javascript - Void Keyword
- Javascript - Page Printing
- JavaScript Objects
- Javascript - Objects
- Javascript - Number
- Javascript - Boolean
- Javascript - Strings
- Javascript - Arrays
- Javascript - Date
- Javascript - Math
- Javascript - RegExp
- Javascript - HTML DOM
- JavaScript Advanced
- Javascript - Error Handling
- Javascript - Validations
- Javascript - Animation
- Javascript - Multimedia
- Javascript - Debugging
- Javascript - Image Map
- Javascript - Browsers
- JavaScript Useful Resources
- Javascript - Questions And Answers
- Javascript - Quick Guide
- Javascript - Functions
- Javascript - Resources
How to check a not-defined variable in JavaScript?
To check a variable is ‘undefined’, you need to check using the following. If the result is “false”, it means the variable is not defined. Here, the variable results in “True” −
Example
<html>
<body>
<script>
var points = 100;
if(points){
document.write("True");
}else{
document.write("False");
}
</script>
</body>
</html>
- Related Articles
- How can I check whether a variable is defined in JavaScript?
- Haskell Program to check whether a variable is defined or not
- How to check if a JavaScript function is defined?
- How to check if a variable exists in JavaScript?
- How to check if a variable is NaN in JavaScript?
- How to check if a variable is boolean in JavaScript?
- How to check for “undefined” variable in JavaScript?
- How can I check if a JavaScript function is defined?
- How to check if a variable is an integer in JavaScript?
- How to check if a variable is an array in JavaScript?
- How to check the type of a variable or object in JavaScript?
- Variable defined with a reserved word const can be changed - JavaScript?
- How can we store a value in user-defined variable?
- How do you check if a variable is an array in JavaScript?
- In MySQL, why a client cannot use a user-defined variable defined by another client?
Advertisements