Is Number.IsNaN() more broken than isNaN()

by

isNaN() and Number.isNaN() both test if a value is (or, in the case of isNaN(), can be converted to a number-type value that represents) the NaN value. In other words, “NaN” does not simply mean “this value is not a number”, it specifically means “this value is a numeric Not-a-Number value according to IEEE-754″.

The reason all your tests above return false is because all of the given values can be converted to a numeric value that is not NaN:

Number('')    // 0
Number('   ') // 0
Number(true)  // 1
Number(false) // 0
Number([0])   // 0

The reason isNaN() is “broken” is because, ostensibly, type conversions aren’t supposed to happen when testing values. That is the issue Number.isNaN() is designed to address. In particular, Number.isNaN() will only attempt to compare a value to NaN if the value is a number-type value. Any other type will return false, even if they are literally “not a number”, because the type of the value NaN is number. See the respective MDN docs for isNaN() and Number.isNaN().

If you simply want to determine whether or not a value is of the number type, even if that value is NaN, use typeof instead:

typeof 'RAWRRR' === 'number' // false

More Related Contents:

  1. Understanding members of Symbol – function constructor
  2. Find list of strings that matches a pattern that start with a special character « and end with a special character »
  3. Unable to access React instance (this) inside event handler [duplicate]
  4. How do you check that a number is NaN in JavaScript?
  5. Why does babel rewrite imported function call to (0, fn)(…)?
  6. Spread Syntax ES6
  7. Async function not returning value, but console.log() does: how to do? [duplicate]
  8. ES6 Object Destructuring Default Parameters
  9. Using _ (underscore) variable with arrow functions in ES6/Typescript
  10. Why does isNaN(” “) (string with spaces) equal false?
  11. How to convert a plain object into an ES6 Map?
  12. Scope of Default function parameters in javascript
  13. React useState hook event handler using initial state
  14. Is there a downside to using ES6 template literals syntax without a templated expression?
  15. Transforming a Javascript iterable into an array
  16. “This” within es6 class method [duplicate]
  17. Syntax error in IE using ES6 arrow functions
  18. Get the class name of ES6 class instance
  19. ESCMAScript 6 arrow functions – parentheses around parameter
  20. Delegated yield (yield star, yield *) in generator functions
  21. SyntaxError: ‘import’ and ‘export’ may appear only with ‘sourceType: module’ – Gulp
  22. Property ‘entries’ does not exist on type ‘ObjectConstructor’
  23. How can I alias a default import in JavaScript?
  24. Are ES6 module imports hoisted?
  25. Unable to use Arrow functions inside React component class [duplicate]
  26. How to test an ES6 class that needs jquery?
  27. Not recommended to use “use strict” in ES6?
  28. What can we do with ES6 Generator that we cannot with for loop?
  29. ECMA6 generators: yield promise
  30. ES6 – declare a prototype method on a class with an import statement

Leave a Comment