Algorithm for generating fibonacci numbers, javascript is not that slow after all

Fibonacci.ts

import * as _ from 'lodash'

function sumPreviousTwo(numbers: number[]) {
  let [n2, n1] = _.takeRight(numbers, 2);
  return n2 + n1;
}

export function fibonacci(length: number): number {
  let firstTwoNumbers = [0, 1];

  let numbers = firstTwoNumbers;
  let remainingLength = length - firstTwoNumbers.length;
  _.times(remainingLength, () => numbers.push(sumPreviousTwo(numbers)));

  return numbers[length-1];
}

FibonacciSpec.ts

import {assert} from "chai";
import {fibonacci} from "../src/Fibonacci";

describe('Fibonacci', () => {

  it('first number is 0', () => {
    assert.deepEqual(fibonacci(1), 0);
  });

  it('the second number is 1', () => {
    assert.deepEqual(fibonacci(2), 1);
  });

  it('the third number is 1', () => {
    assert.deepEqual(fibonacci(3), 1);
  });

  it('acceptance test', () => {
    assert.deepEqual(fibonacci(9), 21);
  });

  it('scales, it takes a few ms to calculate the 1477th, which is ~ 1.3e+308!', () => {
      assert.equal(fibonacci(1477), 1.3069892237633987e+308)
  });

});

test result and perfomance measure

  Fibonacci
    ✓ first number is 0 (1ms)
    ✓ the second number is 1
    ✓ the third number is 1
    ✓ acceptance test
    ✓ scales, it takes a few ms to calculate the 1477th, which is ~ 1.3e+308! (2ms)

  5 passing (4ms)


the perf test varies between 1-2 milliseconds measured with hrtime. Seems suspiciously fast.