function mergeLists(head1, head2) {
    let newnode = new SinglyLinkedListNode(0, null)
    let tempnode = newnode
    
    while(head1 !== null && head2 !== null ){
        if(head1.data < head2.data){
            tempnode.next = head1
            head1 = head1.next //inc of head1 linked list
        }else{
            tempnode.next = head2
            head2 = head2.next  //inc of head2 linked list
        }
        tempnode = tempnode.next //inc of newnode
    }
    
    tempnode.next = head1 || head2 // if either head1 is null then tempnode will update with head2 or vice-versa
    
    return newnode.next
}