JavaScript undefined Property
Below is the example of the undefined Property.
- Example:
<script>
var
a =
"Geeksforgeeks"
function
test() {
if
(
typeof
a ===
"undefined"
) {
txt =
"'a' is undefined"
;
}
else
{
txt =
"'a' is defined"
;
}
document.write(txt);
}
test();
</script>
- Output:
'a' is defined
The undefined property is used to check if a value is assigned to a variable or not.
Syntax:
var x; if (typeof x === "undefined") { txt = "x is undefined"; } else { txt = "x is defined"; }
Return Value: It returns ‘defined’ if the variable is assigned any value and ‘undefined’ if the variable is not assigned any value.
More example code for the above property are as follows:
Program 1:
<!DOCTYPE html> < html > < body > < center > < h1 style = "color: green" > GeeksforGeeks </ h1 > < button onclick = "test()" > Press </ button > < h4 > Click on the Press button to check if "a" is defined or undefined. </ h4 > < p id = "gfg" ></ p > < script > function test() { if (typeof a === "undefined") { txt = "'a' is undefined"; } else { txt = "'a' is defined"; } document.getElementById( "gfg").innerHTML = txt; } </ script > </ center > </ body > </ html > |
Output:
Supported Browsers:
- Google Chrome
- Firefox
- Internet Explorer
- Opera
- Safari
Please Login to comment...