Determine if a variable is null or undefined in JavaScript

This post will discuss how to check if a variable is null or undefined in JavaScript.

There are 7 falsy values in JavaScript – false, 0, 0n, '', null, undefined and NaN. A nullish value consists of either null or undefined. This post will provide several alternatives to check for nullish values in JavaScript.

To check for null variables, you can use a strict equality operator (===) to compare the variable with null. This is demonstrated below, where the boolean expression evaluates to true for only for null and evaluates to false for other falsy values.

var x = null;

if (x === null) {

console.log("variable is null");

}

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Similarly, to check specifically for undefined variables, you can use the strict equality operator (===).

var x;

if (x === undefined) {

console.log("variable is undefined");

}

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To check if a variable is either null or undefined, you can merge the above conditions. The following code demonstrates this, where the conditional statement is satisfied only for null or undefined values.

var x = null;

if (x === undefined || x === null) {

console.log("Variable is either null or undefined");

}

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Finally, the standard way to check for null and undefined is to compare the variable with null or undefined using the equality operator (==). This would work since null == undefined is true in JavaScript.

var x = undefined;

if (x == null) {

console.log("Variable is either null or undefined");

}

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That’s all about checking if a variable is null or undefined in JavaScript.

Determine if a variable is null or undefined in JavaScript

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