Algorithms in JavaScript

linked_list.js

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

function List(){
  this.start = null;
  this.end = null;
  
  // add a node to the list 
  this.append = function(data){
    var node = new Node(data);
    if (this.start === null){
      this.start = node;
      this.end = this.start;
    } else {
      this.end.next = node;
      this.end = this.end.next;
    }
  }

  // iterate over the list, calling `cb` for each node 
  this.walk = function(cb, iter){
    var iter = iter || this.start;
    cb(iter.data, iter.next);
    if (iter.next){
      this.walk(cb, iter.next)
    }
  }

  // find the nth item in the list
  this.nth = function(n){
    function find(i, iter){
      if (i == n) return iter;
      if (iter.next) {
        i++;
        return find(i, iter.next);
      }
      return;
    }
    return find(0, this.start);
  }

}

// TEST IT

var list = new List();

list.append("one")
list.append("two")
list.append("three")
list.append("four")
list.append("five")
list.append("six")

list.walk(function(data, next){
  console.log(data, '->', (next) ? next.data : 'undefined');
});

console.log("---")

console.log( (list.nth(0)).data ); // 'one'
console.log( (list.nth(4)).data ); // 'five'
console.log( list.nth(34) ); // undefined

queue.js

//
// FIFO queue (first in first out)
//
var q = [];

function enqueue(item, queue){
  queue[queue.length] = item
  return queue;
}

function dequeue(queue){
  var ret = [];
  for(var i=1; i<queue.length; i++){
    ret[i-1] = queue[i];
  }
  return ret;
}

// using builtin methods
function enqueue(item, queue){
  queue.push(item)
  return queue;
}

function dequeue(queue){
  queue.shift()
  return queue;
}


q = enqueue(1, q);
q = enqueue(2, q);
q = enqueue(3, q);
q = enqueue(4, q);

if (String(q) == '1,2,3,4') console.log('true');

q = dequeue(q)
q = dequeue(q)
q = dequeue(q)

if (String(q) == '4') console.log('true');

stack.js

//
// LIFO stack (last in first out)
// 

var s = [];

function push(item, stack){
  stack[stack.length] = item;
  return stack;
}

function pop(stack){
  var ret = []
  for(var i=0; i<stack.length-1; i++){
    ret[i] = stack[i]
  }
  return ret;
}

// using builtin methods

function push(item, stack){
  stack.push(item)
  return stack
}

function pop(stack){
  stack.pop()
  return stack;
}


s = push(1, s)
s = push(2, s)
s = push(3, s)
s = push(4, s)


if (String(s) == '1,2,3,4') console.log('true');

s = pop(s)
s = pop(s)
s = pop(s)

if (String(s) == '1') console.log('true');

queue.js and stack.js are both functional programming and don't mutate state. Also they both have manual methods and methods that use builtin javascript functions like pop, push, shift.