JavaScript undefined Property
Last Updated :
08 Feb, 2023
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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:
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:
<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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