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 ="Geeksforneveropen"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"> neveropen </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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