List.ts

interface INode {
  data: number;
  next: INode | null;
}

class LinkedList {
  private _head: INode | null;

  public insert(value: number, index: number) {}

  public prepend(value: number) {
    const node = this.createNode(value);

    if (!this._head) {
      this._head = node;
    } else {
      node.next = this._head;
      this._head = node;
    }
  }

  public append(value: number) {
    const newNode = this.createNode(value);
    let currNode = this._head;

    if (this._head === null) {
      this._head = newNode;
    } else {
      while (currNode.next) {
        currNode = currNode.next;
      }

      currNode.next = newNode;
    }
  }

  public toString() {
    let result: string = "";
    let node: INode | null = this._head;

    while (node) {
      result += `${node.data} -> `;

      node = node.next;
    }

    result += "nil";

    return result;
  }

  public recToString() {
    return this.recToStringHelper(this._head);
  }

  private recToStringHelper(node: INode | null, str: string = "") {
    if (!node) return (str += "nil");

    return this.recToStringHelper(node.next, (str += `${node.data} -> `));
  }

  private createNode(value: number) {
    return {
      data: value,
      next: null
    };
  }
}

var list = new LinkedList();

list.prepend(5);
list.prepend(10);
list.prepend(15);
list.append(30);

list.recToString(); /*?*/