typeof Operator

The typeof operator tells the data type of a given variable. The typeof operator returns one of the following strings:

Returned Value	Meanings
"undefined"	if the value is undefined
"boolean"	if the value is a Boolean
"string"	if the value is a string
"number"	if the value is a number
"object"	if the value is an object or null
"function"	if the value is a function

 
<!DOCTYPE html>
<html>
<head>
    <title>typeof Example</title>
    <script type="text/javascript">

    var aString = "string";
    //The typeof is an operator and not a function, no parentheses are required. 
    document.writeln(typeof aString);    //"string"
    document.writeln(typeof(aString));   //"string" 
    document.writeln(typeof 10);         //"number"
      
    </script>
</head>
<body>
</body>
</html>

Click to view the demo

Calling typeof null returns a value of "object"

 
<!DOCTYPE html>
<html>
<head>
    <title>typeof Example</title>
    <script type="text/javascript">

        var aString = null;
        document.writeln(typeof aString);    //"object"
      
    </script>
</head>
<body>
</body>
</html>

Click to view the demo

The following code calls typeof on an undefined variable.

 
<!DOCTYPE html>
<html>
<head>
    <title>typeof Example</title>
    <script type="text/javascript">

        var aString;
        document.writeln(typeof aString);    //"undefined"
      
    </script>
</head>
<body>
</body>
</html>

Click to view the demo