SLL_Node created by ValentynaGorbachenko - https://repl.it/Dq2c/31

SLL_Node.js

function SLL(){
	this.head = null;
}

function Node(val){
	this.val = val;
	this.next = null;
}

Node.prototype.add = function(val){
	// check if it is not a null and add it to the next pointer
	if(this){
		var temp = this.next;
		this.next = new Node(val);
		this.next.next = temp;
	}
	return this;
};

SLL.prototype.add = function(val){
	// check if sll in not empty
	if (this.head){
		var curr = this.head;
		var prev = null;
		// find the element that points to null
		while(curr.next){
			prev = curr;
			curr = curr.next;
		}
		// console.log("curr ", curr);
		if(curr.deleted){
			prev.next = new Node(val);
		}
		curr.next = new Node(val);
	} else {
		this.head = new Node(val);
	}
	return this;
};

SLL.prototype.find = function(val){
	if(this.head){
		var curr = this.head;
		while(curr){
			if(curr.val == val){
				return curr;
			}
			curr = curr.next;
		}
	}
	return null;
};

Node.prototype.remove = function(){
	// check if node is not null
	// check if node.next exist
	if(this){
		if(this.next){
			// copy value from the next node to current
			// relink to the next after next
			this.val = this.next.val;
			this.next = this.next.next;
		
		} else {
			this.val = undefined;
			this.deleted = true;
		}
		return true;
	}
	return false;
};

SLL.prototype.remove = function(val){
	if(!this.head){ return this; }
	var curr = this.head;
	// if value is in the first node
	if (curr.val == val) {
		// console.log("head")
		if(this.head.next){
			// console.log(curr.next);
			this.head = curr.next;
		} else {
			this.head = null;
		}
		
		return this;
	}
	
	while(curr.next !== null && curr.next.val !== val){
		curr = curr.next;
	}
	if(curr.next.val == val){
		curr.next = curr.next.next;
	}
	return this;
};

SLL.prototype.detectLoop = function(){
	if(!this.head){ return false;}
	var slow = this.head,
		fast = this.head.next;
	while(slow !== fast && fast !== null){
		fast = fast.next;
		if(fast){
			fast = fast.next;
			slow = slow.next;
		}
	}
	return slow == fast;
};

SLL.prototype.fixLoop = function(){
	if(!this.head){ return this;}
	var slow = this.head,
		fast = this.head.next;
	while(slow !== fast && fast !== null){
		fast = fast.next;
		if(fast){
			fast = fast.next;
			slow = slow.next;
		}
	}
	if(slow == fast){
		slow = this.head;
		while(slow != fast.next){
			slow = slow.next;
			fast = fast.next;
		}
		fast.next = null;
		console.log("loop fixed, last element in the list is ", fast);
	} else {
		console.log("there were no loop");
	}
	return this;
};

Node.prototype.printReverseNode = function(){
	if (!this) { return;}
	if(this.next) {
		this.next.printReverseNode();
		console.log("printing in reverse order ",this.val);
	} else {
		console.log("printing in reverse order ",this.val);
	}
};

SLL.prototype.printReverse = function(){
	if(!this.head) { return; }
	this.head.printReverseNode();
};

SLL.prototype.midPont = function(){
	if(!this.head){ return null;}
	var slow = this.head,
		fast = this.head.next;
	while(fast){
		fast = fast.next;
		if(fast){
			slow = slow.next;
			fast = fast.next;
		}
	}
	return slow;
};

SLL.prototype.reverse = function(){
	if(!this.head){ return this;}
	var curr = this.head,
		prev = null,
		next = null;
	while(curr){
		next = curr.next;
		curr.next = prev;
		prev = curr;
		curr = next;
	}
	this.head = prev;
	return this;
};

SLL.prototype.isPalindrom = function(){
	var head = this.head;
	function isPalindromNode(node){
		var temp;
		if(node.next){
			temp = isPalindromNode(node.next);
		} else {
			temp = head;
		}
		if(temp != null && node.val == temp.val){
			if(temp.next == null){
				return true; // return temp;
			} else {
				return temp.next;
			}
		} else { 
			return null;
		}
	}
	if(!this.head){
		return true;
	} else {
		return null != isPalindromNode(this.head);
	}
};




function mergeSLL(list1, list2){
	// merges two lists
}

var list = new SLL();
list.add(1).add(2).add(3);
console.log("list.add(1).add(2).add(3)\n",JSON.stringify(list));
// console.log(list.find(3).remove());
list.remove(3);
console.log("list.remove(3)\n",JSON.stringify(list));


list.add(4).add(5);
console.log("list.add(4).add(5)\n",JSON.stringify(list));
console.log(" list has loop ", list.detectLoop());

list.fixLoop();
list.find(5).next = list.find(2);
console.log("list.find(5).next = list.find(2)");
console.log("list has loop ", list.detectLoop());

list.fixLoop();
console.log("list ufter fix\n",JSON.stringify(list));
list.find(2).add(8).add(7);
console.log("list.find(2).add(8).add(7)\n",JSON.stringify(list));


list.printReverse();
list.reverse();
console.log("list.reverse()\n",JSON.stringify(list)); 
list.reverse();
console.log("list.reverse()\n",JSON.stringify(list)); 
console.log("midPoint is ",list.midPont());

var listPpolindrom = new SLL();
listPpolindrom.add('a').add('b').add('a').add('b');
// var node = listPpolindrom.find('a');
console.log("abab is palindrom", listPpolindrom.isPalindrom());
var listPpolindrom2 = new SLL();
listPpolindrom2.add('a').add('b').add('a');
console.log("aba is palindrom", listPpolindrom2.isPalindrom());