Tryit Editor v2.9

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<!DOCTYPE html>
<html>
<body>

<p>Both the value, and the data type, of a variable with no value is <b>undefined</b>.</p>

<p id="demo"></p>

<script>
var person;
document.getElementById("demo").innerHTML =
person + "<br>" + typeof person;
</script>

</body>
</html>