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How to check for null, undefined, or blank variables in JavaScript?
On getting the result of the following, you can find whether a variable is null or undefined. If the result is “false”, it means the variable is null and undefined.
Here, the variable results in “True” −
<html>
<body>
<script>
var age = 10;
if(age){
document.write("True");
} else{
document.write("False");
}
</script>
</body>
</html>Use “typeof” to check whether a variable exists or not −
<html>
<body>
<script>
var age = 10;
if( typeof age !== 'undefined' ) {
document.write("True");
} else{
document.write("False");
}
</script>
</body>
</html>
Updated on 13-Jun-2020 13:32:12
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