Input: 1 2 3 4 5 
Output: 3 1 2 4 5

Input: 1 2 3 4 5 6
Output: 4 1 2 3 5 6 

<script> 
// Javascript program to make middle node  
// as head of Linked list 
  
// Link list node  
class Node  
{ 
    constructor(val)  
    { 
        this.data = val; 
        this.next = null; 
    } 
} 
  
var head; 
  
// Function to get the middle and set at  
// beginning of the linked list 
function setMiddleHead()  
{ 
    if (head == null) 
        return; 
  
    // To traverse list nodes one 
    // by one 
    one_node = head; 
  
    // To traverse list nodes by 
    // skipping one. 
    two_node = head; 
  
    // To keep track of previous of middle 
    prev = null; 
    while (two_node != null &&  
           two_node.next != null)  
    { 
        // for previous node of middle node  
        prev = one_node; 
  
        // Move one node each time  
        two_node = two_node.next.next; 
  
        // Move two node each time  
        one_node = one_node.next; 
    } 
  
    // Set middle node at head  
    prev.next = prev.next.next; 
    one_node.next = head; 
    head = one_node; 
} 
  
// To insert a node at the beginning of 
// linked list. 
function push(new_data) 
{ 
    // Allocate node  
    new_node = new Node(new_data); 
  
    // Link the old list of the new node  
        new_node.next = head; 
  
    // Move the head to point to the  
    // new node  
    head = new_node; 
} 
  
// A function to print a given linked list 
function printList(ptr)  
{ 
    while (ptr != null)  
    { 
        document.write(ptr.data + " "); 
        ptr = ptr.next; 
    } 
    document.write("<br/>"); 
} 
  
// Driver function  
      
// Create a list of 5 nodes 
head = null; 
var i; 
for (i = 5; i > 0; i--) 
    push(i); 
  
document.write(" list before: "); 
printList(head); 
  
setMiddleHead(); 
  
document.write(" list After:  "); 
printList(head); 
// This code is contributed by aashish1995  
</script> 

list before: 1 2 3 4 5
list After : 3 1 2 4 5