array reverse

index.js

const numElements = 10000;
const numLoops = 100000;

const arr = [];
for (let i = 0; i < numElements; i += 1) {
  arr.push(i);
}

function reverse1(a) {
  const reversed = [];
  const aLength = a.length;
  if (aLength >= 0) {
    for (let i = aLength; i >= 0; i -= 1) {
      reversed.push(a[i]);
    }
    return reversed;
  }
  return a;
}

function reverse2(a) {
  for (let l = 0, m = a.length / 2, r = a.length - 1; l < m; l += 1, r -= 1) {
    const t = a[l];
    a[l] = a[r];
    a[r] = t;
  }
  return a;
}

function reverse3(a) {
  const result = new Array(a.length);
  for (let i = 0, r = a.length - 1; r >= 0; i += 1, r -= 1) {
    result[i] = a[r];
  }
  return result;
}

console.time('Method 1');
for (let i = 0; i < numLoops; i += 1) {
  reverse1(arr);
}
console.timeEnd('Method 1');

console.time('Method 2');
for (let i = 0; i < numLoops; i += 1) {
  reverse2(arr);
}
console.timeEnd('Method 2');

console.time('Method 3');
for (let i = 0; i < numLoops; i += 1) {
  reverse3(arr);
}
console.timeEnd('Method 3');