JavaScript undefined Property

0 0 1 minute read

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 ="Geeksforzambiatek"
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"> 
        zambiatek 
    </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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