JS Built-ins
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ArrayArray.prototype.copyWithinintermediate

Array.prototype.copyWithin() — returns the same array

📖 Usage Example
const arr = [1, 2, 3]
const result = arr.copyWithin(0, 1)
console.log(result === arr)  // → true  (same reference)

copyWithin() mutates the array in place and returns the same array reference.

Array.prototype.copyWithin() — mutation and return value

copyWithin() mutates the original array and returns a reference to that same array (not a copy). This means the returned value and the original variable both point to the same array.

Challenge: Implement isSameArray(arr) that returns true when the result of calling arr.copyWithin(0, 1) is the exact same reference as arr.

isSameArray([1, 2, 3]) // → true
💡 Hints (2)
  • • `===` checks reference equality — it returns `true` only if both sides are the same object in memory.
  • • Unlike `map` or `filter`, `copyWithin` returns the original array, not a new one.