JS Built-ins
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TypeCoercionintermediate

NaN Behavior

NaN (Not a Number)

NaN is a special numeric value resulting from invalid operations:

  • Number('abc') is NaN
  • parseInt('x') is NaN
  • 0 / 0 is NaN

Important: NaN !== NaN — NaN is the only value not equal to itself!

  • Use Number.isNaN(x) to reliably check for NaN
  • typeof NaN is 'number' (quirk of JavaScript)

Challenge: Verify NaN's unique behavior.

💡 Hints (4)
  • • NaN is a special numeric value that does not equal itself.
  • • Always use Number.isNaN() to check for NaN, not === or the global isNaN().
  • • typeof NaN returns "number", which is technically correct but unintuitive.
  • • NaN stands for "Not a Number" but its type is still "number".