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Fibonacci Number(s)

The Toolbox offers multiple utilities for working with the Fibonacci sequence:

  • Generate full sequences
  • Fetch a specific Fibonacci number
  • Lazily iterate using a generator
  • Supports aliases for convenient use

All inputs are coerced and validated using Number().

getFibonacciSeries​

Generates the first limit Fibonacci numbers iteratively.

Function Signature​

function getFibonacciSeries(limit: Numeric): number[];

Parameters​

  • limit — Number of Fibonacci numbers to generate.

Returns​

An array of Fibonacci numbers from index 0 to limit - 1. If the input is invalid or non-positive, an empty array is returned.

Example​

getFibonacciSeries(7); // [0, 1, 1, 2, 3, 5, 8]

Aliases​

  • getFibonacci
  • getFibonacciNumbers

getFibonacciSeriesMemo​

Generates the first limit Fibonacci numbers using recursion with memoization.

Function Signature​

function getFibonacciSeriesMemo(limit: Numeric): number[];

Parameters​

  • limit — Number of Fibonacci numbers to generate.

Returns​

An array of Fibonacci numbers from index 0 to limit - 1, using a memoized recursive function. Invalid input returns an empty array.

Example​

getFibonacciSeriesMemo(7); // [0, 1, 1, 2, 3, 5, 8]

Aliases​

  • getMemoizedFibonacci
  • getMemoizedFibonacciSeries

fibonacciGenerator​

A lazy generator that yields Fibonacci numbers up to a given limit.

Function Signature​

function* fibonacciGenerator(
  limit: Numeric,
  onYield?: (value: number, index: number) => void
): Generator<number, void, void>;

Parameters​

  • limit — Number of Fibonacci values to yield.
  • onYield (optional) — Callback called on each yield with (value, index).

Returns​

  • A generator that yields Fibonacci numbers one by one up to the specified limit.

Example​

for (const value of fibonacciGenerator(5)) {
  console.log(value);
}
// Output: 0, 1, 1, 2, 3

With Callback​

fibonacciGenerator(3, (val, idx) => {
  console.log(`Index ${idx} => ${val}`);
});

Aliases​

  • generateFibonacci

getNthFibonacci​

Returns the Fibonacci number at the specified index.

Function Signature​

function getNthFibonacci(index: Numeric): number;

Parameters​

  • index — Index (0-based) of the Fibonacci number to retrieve.

Returns​

  • The Fibonacci number at the given index.

Example​

getNthFibonacci(8); // 21

Summary of Aliases​

FunctionAliases
getFibonacciSeriesgetFibonacci, getFibonacciNumbers
getFibonacciSeriesMemogetMemoizedFibonacci, getMemoizedFibonacciSeries
getNthFibonacciNone
fibonacciGeneratorgenerateFibonacci

Notes​

  • All functions gracefully handle invalid or non-numeric inputs.
  • Internally, inputs are coerced using Number(...), and validation is performed via Number.isFinite(...).
  • The memo version avoids recalculation via Map, but not tail-call optimized.
  • The memoized variant is optimal for moderate limit values but not designed for very large n due to recursion depth limits.
  • The generator is memory-efficient and supports optional side effects per iteration.
  • Generator is ideal for performance-sensitive or infinite-like iteration use cases.

Limitations​

  • fibonacciGenerator() does not return (short-circuits early) if limit < 0 or not finite.
  • Recursive memoized version is not tail-optimized; it may hit stack limits on very high input values.
  • getNthFibonacci() uses an iterative approach, so it performs efficiently for most practical input ranges.
  • Floating-point limits apply at high index values (n > 70).

Summary​

These Fibonacci utilities are flexible and efficient for different use cases — whether generating an entire sequence, computing a single term, or lazily consuming values via a generator.