Implement Trie (Prefix Tree)

class TrieNode {
  private readonly _char: string;
  private _isEnd: boolean;
  private readonly children: Map<string, TrieNode>;
 
  constructor(char: string) {
    this._char = char;
    this._isEnd = false;
    this.children = new Map();
  }
 
  get char() {
    return this._char;
  }
 
  get isEnd() {
    return this._isEnd;
  }
 
  set isEnd(value: boolean) {
    this._isEnd = value;
  }
 
  getChildNode(char: string): TrieNode | undefined {
    return this.children.get(char);
  }
 
  addChildNode(char: string): TrieNode {
    const newChildNode = new TrieNode(char);
    this.children.set(char, newChildNode);
    return newChildNode;
  }
}
 
export class Trie {
  private readonly root: TrieNode;
 
  constructor() {
    this.root = new TrieNode('');
  }
 
  insert(word: string): void {
    let currentNode = this.root;
    for (const char of word) {
      currentNode = currentNode.getChildNode(char) ?? currentNode.addChildNode(char);
    }
    currentNode.isEnd = true;
  }
 
  search(word: string): boolean {
    let currentNode = this.root;
    for (const char of word) {
      const nextNode = currentNode.getChildNode(char);
      if (!nextNode) {
        return false;
      }
      currentNode = nextNode;
    }
    return currentNode.isEnd;
  }
 
  startsWith(prefix: string): boolean {
    let currentNode = this.root;
    for (const char of prefix) {
      const nextNode = currentNode.getChildNode(char);
      if (!nextNode) {
        return false;
      }
      currentNode = nextNode;
    }
    return true;
  }
}