Use typeof method with the not equal operator to check if a variable is defined and not empty in JavaScript.
if( typeof myVar !== 'undefined' && myVar != null){
// myVar is undefined or null
}Or syntax for checking null or undefined or empty
if (typeof value !== 'undefined' && value) {
//deal with value'
};JavaScript checks if a variable is defined and not empty
Simple example code.
<!DOCTYPE html>
<html>
<body>
<script>
var myVar = 0
if( typeof myVar !== 'undefined' && myVar != null ){
console.log(myVar)
}
</script>
</body>
</html>
Output:
Even if the value is 0, this will execute but this will pass an undefined variable.
var myVar;
if (myVar !== null) {
console.log(myVar)
}If you don’t want it to execute when it’s 0, then set it as
if (myVar) {...}Do comment if you have any doubts or suggestions on this JS variable topic.
Note: The All JS Examples codes are tested on the Firefox browser and the Chrome browser.
OS: Windows 10
Code: HTML 5 Version