Flatten a nested array

Turn a nested array into one sequence of values.

JavaScript Version 1.0.0 · MIT · .md

function flatten(values) { return values.flat(Infinity); }

Input & expected output

[
  1,
  [
    2,
    [
      3
    ]
  ],
  4
]

[
  1,
  2,
  3,
  4
]

The edge case

[
  [],
  [
    1,
    []
  ]
]

[
  1
]

Know the limits

• Input depth is capped at 12 and the total element count at 1,000 in this lab.
• Array holes are skipped. JSON input cannot represent holes.

The function above is the implementation used by the lab. The lab validates JSON types and caps size before execution; include equivalent validation when accepting untrusted input in your application.

Keep exploring

• Clone an array — Create a new array without copying the objects inside it.
• Remove duplicate values — Keep the first occurrence of each value, in its original order.
• Split an array into chunks — Build consecutive chunks without changing the original array.