Find the index of the maximum item of an array

Return the index of the first largest number.

JavaScript Version 1.0.0 · MIT · .md

function indexOfMax(values) { return values.reduce((best, value, i) => (value > values[best] ? i : best), 0); }

Input & expected output

[
  1,
  3,
  9,
  7,
  9
]

2

The edge case

[]

0

Know the limits

• The first maximum wins on ties. An empty array returns 0, as in the original — check the length first.

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.
• Flatten a nested array — Turn a nested array into one sequence of values.