This is a long-standing bug in JavaScript, but since lots of codes on the web written around this behavior, and thus fixing it would create a lot more problem, so idea of fixing this issue was abandoned by the committee that design and maintains JavaScript. This means you are supposed to be able to check if a variable is null with the typeof () method. It’s a new feature introduced in JavaScript ES2020 that allows you to check for null or undefined values in a more concise way. If you try to test the null values using the typeof operator it will not work as expected, because JavaScript return "object" for typeof null instead of "null". This operator is also known as the Nullish Coalescing Operator. You assign a null to a variable with the intention that currently this variable does not have any value but it will. In JavaScript if a variable has been declared, but has not been assigned a value, is automatically assigned the value undefined. Why is isNaN(null) false in JS - The isNan() method is used in JavaScript to check whether there’s the existence of an undefined value or can say checks for a NaN object. null is not an identifier for a property of the global object, like undefined can be. Try it Syntax null Description The value null is written with a literal: null. It is one of JavaScript's primitive values and is treated as falsy for boolean operations. * Since null = undefined is false, the following statements will catch only null or undefined */Īlert('Variable "comment" is undefined.') The null value represents the intentional absence of any object value. other code that would catch the exception, either run the rest of the code after the loop correctly, or throw the null exception in some line, so it will behave the same. * Since null = undefined is true, the following statements will catch both null and undefined */Īlert('Variable "firstName" is undefined.') Most of old code would check for null already, so it will not be affected. Var comment = document.getElementById('comment') Ĭonsole.log(firstName) // Print: undefinedĬonsole.log(typeof firstName) // Print: undefinedĬonsole.log(typeof lastName) // Print: objectĬonsole.log(typeof comment) // Print: objectĬonsole.log(null = undefined) // Print: trueĬonsole.log(null = undefined) // Print: false
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