function(target, vertex) {
      vertex.prev = target;
      vertex.next = target.next;

      if (vertex.next === null) {
        this.tail = vertex;
      } else {
        vertex.next.prev = vertex;
      }

      target.next = vertex;

      return this;
    }
function(target, vertex) {
      vertex.prev = target;
      vertex.next = target.next;

      if (vertex.next === null) {
        this.tail = vertex;
      } else {
        vertex.next.prev = vertex;
      }

      target.next = vertex;

      return this;
    }
function ( target , vertex ) { vertex . prev = target ; vertex . next = target . next ; if ( vertex . next === null ) { this . tail = vertex ; } else { vertex . next . prev = vertex ; } target . next = vertex ; return this ; }
Inserts a vertex after the target vertex
Inserts a vertex after the target vertex