Javascript linked list complexity demo

linked-list.js

var now;
if (typeof performance !== 'undefined') {
  // In the browser.
  now = function () {
    return performance.now() * 1E-3;
  }
} else {
  // In node.
  now = function () {
    var hr = process.hrtime();
    return hr[0] + hr[1] * 1E-9;
  } 
}

//------------------------------------------------------------------------------
// Simple singly linked list
//------------------------------------------------------------------------------

var NO_NODE = null;

function Node(value, next) {
  this.value = value;
  this.next = next;
}

function List() {
  this.head = NO_NODE;
}

List.prototype.toString = function () {
  var string = '[';
  for (var node = this.head; node; node = node.next) {
    string += node.value;
    if (node.next) string += ', ';
  }
  string += ']';
  return string;
}

List.prototype.unshift = function (value) {
  // Replace the head with our new node, with the old head following it.
  this.head = new Node(value, this.head);
}

List.prototype.push = function (value) {
  // Create the new node for this value.  Since it will be the last element
  // on the list, it has no next node.
  var newNode = new Node(value, NO_NODE);

  if (this.head === NO_NODE) {
    // This is the first element in the list, so the new node is the head node.
    this.head = newNode;
  } else {
    // Find the last node in the list, by starting at the head node and walking
    // down the list until we find one that has no next node.
    var tail = this.head;
    while (tail.next !== NO_NODE) tail = tail.next;
    // The new node comes after the old tail node.
    tail.next = newNode;
  }
}

//------------------------------------------------------------------------------

/**
 * Constructs a linked list of the numbers 0 through n - 1.
 * 
 * Uses `List.prototype.push`.
 */
function countPush(n) {
  var numbers = new List();
  for (var i = 0; i < n; ++i) numbers.push(i);
  return numbers;
}

console.log("countPush:")
for (var n = 1000; n <= 25000; n += 1000) {
  var start = now();
  var numbers = countPush(n);
  var end = now();
  console.log(n, end - start);
}

//------------------------------------------------------------------------------

/**
 * Constructs a linked list of the numbers 0 through n - 1.
 * 
 * Uses `List.prototype.unshift`.
 */
function countUnshift(n) {
  var numbers = new List();
  for (var i = n - 1; i >= 0; --i) numbers.unshift(i);
  return numbers;
}

console.log("\ncountUnshift:")
for (var n = 1000; n <= 25000; n += 1000) {
  var start = now();
  var numbers = countUnshift(n);
  var end = now();
  console.log(n, end - start);
}