We're pretty aware, generally that JavaScript is weird, but did you know Not-A-Number (NaN) is a type of number? Mat Marquis walks us through why that is and how to deal with NaN well in your codebases.

Piccalilli's resource offers insights, tutorials, and resources for frontend developers and web designers. Readers can learn about HTML, CSS, and JavaScript techniques, as well as design principles and accessibility. With articles, tutorials, and design showcases, Piccalilli provides  guidance and inspiration for creating modern and accessible web experiences.

Piccalilli

NaN in JavaScript is paradoxically a number type that represents non-numeric calculation results. It propagates through arithmetic operations, always returning NaN, and uniquely isn't equal to itself (NaN !== NaN). This behavior stems from IEEE floating-point standards where NaN acts as an error state. Two methods exist for checking NaN: the global isNaN() coerces values before checking, while Number.isNaN() checks for explicit NaN values without coercion. Understanding this distinction is crucial for proper type validation in calculations.

NaN, the not-a-number number that isn’t NaN