JS Built-ins
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ArrayArray.prototype.includesintermediate

Array.prototype.includes() — finding NaN

📖 Usage Example
const arr = [1, NaN, 3]
arr.includes(NaN)  // → true  (uses SameValueZero)
arr.indexOf(NaN)  // → -1   (does not find NaN)

Use includes() to check for NaN — unlike indexOf(), it handles NaN correctly.

Array.prototype.includes() — SameValueZero

Unlike indexOf, which uses strict equality (===), includes() uses SameValueZero, which correctly identifies NaN as equal to itself. So [NaN].includes(NaN) returns true.

Challenge: Implement hasNaN(arr) that returns arr.includes(NaN).

hasNaN([1, NaN, 3]) // → true
hasNaN([1, 2, 3])   // → false
💡 Hints (2)
  • • `NaN === NaN` is `false` in JavaScript, so `indexOf` cannot find it.
  • • `includes()` uses SameValueZero, which treats `NaN` as equal to `NaN`.