How to check for an undefined or null variable in JavaScript?
If you also want to check for falsy values (like 0, "", false, NaN), you can use: if (!some_variable) { // do stuff } However, if you only care about null and undefined, if (some_variable == null) is best.
Javascript variable checking: (null or undefined) vs boolean
Jun 8, 2017 · I want to check in an JS object (example: { x:false, y:true } ) if some properties are either boolean or if they are (null || undefined). Is there an easy way in JS or Underscore to …
javascript - why null is not converted to a boolean value in a ...
Nov 9, 2015 · From MDN: Logical AND (&&) expr1 && expr2 Returns expr1 if it can be converted to false; otherwise, returns expr2. Thus, when used with Boolean values, && returns true if …
null, undefined, NaN, and false in Javascript - Sling Academy
Feb 20, 2023 · NaN (stands for not a number) and false are both used to represent a non-true condition, but NaN specifically represents an invalid number result, while false represents a …
How to check for null, undefined or blank Variables in JavaScript
May 7, 2023 · In this article, we will explore the standards and best practices for checking for these types of variables in JavaScript. Null: A variable that is null has been explicitly set to …
JavaScript Nullable – How to Check for Null in JS
Jul 7, 2022 · null == undefined evaluates as true because they are loosely equal. null === undefined evaluates as false because they are not, in fact, equal. <null_variable> === null is …
javascript - Falsy values vs null, undefined, or empty string ...
Dec 16, 2015 · Is there a standard function to check for null, undefined, or blank variables in JavaScript? The set of "truthy" and "falsey" values in JavaScript comes from the ToBoolean …
Undefined Vs Null in JavaScript - GeeksforGeeks
Sep 17, 2024 · undefined indicates a variable hasn’t been initialized, while null is intentionally assigned to indicate no value. Understanding the distinction helps write cleaner, more …
How do I check for an empty/undefined/null string in JavaScript?
Mar 10, 2025 · In this detailed guide, we will explore multiple effective ways how to check for empty, undefined, or null strings in JavaScript. Specifically, we will cover the usage of the …
How to check if value is undefined or null in JavaScript
Jun 8, 2023 · Checking for Undefined or Null Using the Equality Operator (==) The easiest way to check if a value is either undefined or null is by using the equality operator (==). The equality …
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