queue-with-two-stacks.js

var stack1 = [];
var stack2 = [];

function isEmptyStack(stack) {
  return stack.length === 0;
}

function enqueue(obj) {
  return stack1.push(obj);
}

function dequeue() {
  if (!isEmptyStack(stack2)) {
    return stack2.pop();
  } else {
    return (function transfer() {
      if (isEmptyStack(stack1)) {
        return stack2.pop();
      } else {
        stack2.push(stack1.pop());
        return transfer();
      }
    })();
  }
}