inserafternode.js

    insertAfter(key, data) {
       /*
       If list is empty
       */
        if (this.head == null) {
            console.log("The list is empty");
        }
      
       /*
       Travese through the list until `key`
       matches with `data` of the `currentnode` 
       and then point `next` of newly created `node`
       to the `next` of `cuurentnode` and then point `next` 
       of `currentnode` to the newly created `node`.
       */
        else {
            let currentNode = this.head;
            let newNode = new node(data);
            while (currentNode != null) {
                if (currentNode.data == key) {
                    // point `next` of newly created `node` to the `next` of `currentnode`
                    newNode.next = currentNode.next;
                    //  point `next` of `currentnode` to the newly created `node`
                    currentNode.next = newNode;
                    break;
                }
                currentNode = currentNode.next;
            }
        }
        /*
        length is incremented.
        */
        this.length++;

    }