Calculate Fibonacci numbers

Return the nth Fibonacci number with memoized recursion.

JavaScript Version 1.0.0 · MIT · .md

function fibonacci(n, memo = {}) { return memo[n] || (n <= 2 ? 1 : (memo[n] = fibonacci(n - 1, memo) + fibonacci(n - 2, memo))); }

Input & expected output

10

55

The edge case

78

8944394323791464

Know the limits

• The lab stops at n = 78, the largest Fibonacci number below Number.MAX_SAFE_INTEGER; use BigInt beyond it.
• fibonacci(1) and fibonacci(2) are 1; n = 0 also returns 1 here.

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

• Clamp a number to a range — Keep a number inside an inclusive minimum and maximum.
• Round to a number of digits — Apply decimal scaling and JavaScript rounding for display-oriented values.
• Add an ordinal suffix to a number — Append st, nd, rd or th to a positive integer.