Check if a flat array has duplicate values

Compare the size of a Set with the array length.

JavaScript Version 1.0.0 · MIT · .md

function hasDuplicates(values) { return new Set(values).size !== values.length; }

Input & expected output

[
  "[email protected]",
  "[email protected]",
  "[email protected]"
]

true

The edge case

[]

false

Know the limits

• Values use SameValueZero: NaN equals NaN, and objects compare by reference.
• Example: a repeated recipient. On Oveyon’s /v1/send each recipient is one quota unit, so deduplicate before sending.

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

• Check whether all values are equal — Compare every item with the first using Object.is.
• Check whether an object is empty — Check for own enumerable string keys on a JSON object.
• Check whether an integer is even — Test parity for safe integers, including zero and negative values.