2-1.js

function Node(d) {

  this.next = undefined;
  this.data = d;
  
  this.appendToTail = function(d) {
    var end = new Node(d);
    var n = this;
    while (n.next !== undefined) { n = n.next; }
    n.next = end;
  };
  this.removeDups = function() {
    var hash = [];
    var current = this;
    var prev;
    while (current !== undefined) { 
      if(hash[current.data]) {
        //remove 
        prev.next = current.next;
      } else {
        hash[current.data] = true;
        prev = current;
      }

      current = current.next; 
    }
    
  };
  this.print = function() {
    console.log("------");
    var n = this;
    console.log(n.data);
    while (n.next !== undefined) { 
      n = n.next; 
      console.log(n.data);
    }
    console.log("------");
  };
}

var root = new Node(5);
root.appendToTail(3);
root.appendToTail(3);
root.appendToTail(3);
root.appendToTail(3);
root.appendToTail(3);
root.appendToTail(4);
root.appendToTail(7);
root.appendToTail(4);
root.appendToTail(1);
root.appendToTail(3);
root.print();
root.removeDups();
root.print();