JS Built-ins
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ArrayArray.isArrayintermediate

Array.isArray() — check if all elements are arrays

📖 Usage Example
const matrix = [[1, 2], [3, 4]]
matrix.every(Array.isArray)  // → true  (all rows are arrays)

Use Array.isArray with every() to confirm all elements of an array are themselves arrays.

Array.isArray() — array of arrays

Using Array.isArray together with .every() lets you verify that every element of an array is itself an array — a useful validation when working with matrix data.

Challenge: Implement isArrayOfArrays that returns true only when the input is an array and every element is also an array.

isArrayOfArrays([[1, 2], [3, 4]]) // → true
isArrayOfArrays([[1], 2, [3]])    // → false
isArrayOfArrays([])               // → true  (vacuously true)
💡 Hints (2)
  • • First guard with `Array.isArray(val)`, then chain `.every(Array.isArray)` on the result.
  • • `.every()` short-circuits on the first failing element.