Implementation of Queue in JS

queueInJs.js

function Queue() {
  this.length = 0;
}

Queue.prototype.push = function (item) {
  var node = {item: item};
  if (this.last) {
    this.last = this.last.next = node;
  } else {
    this.last = this.first = node;
  }
  this.length++;
};

Queue.prototype.shift = function () {
  var node = this.first;
  if (node) {
    this.first = node.next;
    if (!(--this.length)) {
      this.last = undefined;
    }
    return node.item;
  }
};

Queue.prototype.slice = function (start, end) {
  start = typeof start === 'undefined' ? 0 : start;
  end = typeof end === 'undefined' ? Infinity : end;

  var output = [];

  var i = 0;
  for (var node = this.first; node; node = node.next) {
    if (--end < 0) {
      break;
    } else if (++i > start) {
      output.push(node.item);
    }
  }
  return output;
}

module.exports = Queue;