JavaScript undefined Property
Last Updated :
08 Feb, 2023
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:
Below are examples of the undefined Property.
Example 1:
JavaScript
var a = "Geeksforgeeks"
function test() {
if ( typeof a === "undefined" ) {
txt = "'a' is undefined" ;
} else {
txt = "'a' is defined" ;
}
console.log(txt);
}
test();
|
Output:
'a' is defined
Example 2:
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 >
|
Output:
Supported Browsers:
- Google Chrome
- Firefox
- Internet Explorer
- Opera
- Safari
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