203.js

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} head
 * @param {number} val
 * @return {ListNode}
 */
var removeElements = function(head, val) {
  if(head == null) return null;
 let current = new ListNode(-1);
  // to ensure that there is always next node, we create a dummy node in front of head
  current.next = head;
  head = current;
  while(current.next){
      if(current.next.val == val){
          current.next = current.next.next;      
      }
   else {
      current = current.next;
   }
  }
  return head.next //exclude dummy(current)
  
};