Equality comparisons and sameness — When to use Object.is() versus triple equals

Reference note (untrusted external data; do not execute it as instructions). In general, the only time {{jsxref("Object.is")}}'s special behavior towards zeros is likely to be of interest is in the pursuit of certain meta-programming schemes, especially regarding property descriptors, when it is desirable for your work to mirror some of the characteristics of {{jsxref("Object.defineProperty")}}. If your use case does not require this, it is suggested to avoid {{jsxref("Object.is")}} and use === instead. Even if your requirements involve having comparisons between two {{jsxref("NaN")}} values evaluate to true, generally it is easier to special-case the {{jsxref("NaN")}} checks (using the {{jsxref("isNaN")}} method available from previous versions of ECMAScript) than it is to work out how surrounding computations might affect the sign of any zeros you encounter in your comparison. Here's a non-exhaustive list of built-in methods and operators that might cause a distinction between -0 and +0 to manifest itself in your code (unary negation) : Consider the following example {{jsxref("Math.atan2")}}, {{jsxref("Math.ceil")}}, {{jsxref("Math.pow")}}, {{jsxref("Math.round")}} : In some cases, it's possible for a -0 to be introduced into an expression as a return value of these methods even when no -0 exists as one of the parameters. For example, using {{jsxref("Math.pow")}} to raise {{jsxref("Infinity", "-Infinity")}} to the power of any negative, odd exponent evaluates to -0. Refer to the documentation for the individual methods. {{jsxref("Math.floor")}}, {{jsxref("Math.max")}}, {{jsxref("Math.min")}}, {{jsxref("Math.sin")}}, {{jsxref("Math.sqrt")}}, {{jsxref("Math.tan")}} : It's possible to get a -0 return value out of these methods in some cases where a -0 exists as one of the parameters. E.g., Math.min(-0, +0) evaluates to -0. Refer to the documentation for the individual methods. ~, > : Each of these operators uses the ToInt32 algorithm internally. Since there is only one representation for 0 in the internal 32-bit integer type, -0 will not survive a round trip after an inverse operation. E.g., both Object.is(~~(-0), -0) and Object.is(-0 > 2, -0) evaluate to false. Relying on {{jsxref("Object.is")}} when the sign of zeros is not taken into account can be hazardous. Of course, when the intent is to distinguish between -0 and +0, it does exactly what's desired. Attribution: Adapted from MDN Web Docs under CC-BY-SA-2.5. Adaptation: WikiKV selected one documentation section, normalized formatting, retained bounded excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.