Hash Table in Typescript.

class HashNode<T> {
    constructor(public key: string, public value: T, public next: HashNode<T> | null = null) { }
}

export class HashTable<T> {
    private _bucketList: Array<HashNode<T> | null>;

    constructor(size: number) {
        this._bucketList = new Array<HashNode<T> | null>(size);
    }

    private hash = (key: string): number => {
        let hashCode: number = 0;
        for (let i: number = 0; i < key.length; i++) {
            hashCode += key.charCodeAt(i);
        }
        return hashCode % this._bucketList.length;
    }

    public insert = (key: string, value: T): void => {
        const index: number = this.hash(key);
        if (!this._bucketList[index])
            this._bucketList[index] = new HashNode<T>(key, value);
        else if (this._bucketList[index]!.key === key)
            this._bucketList[index]!.value = value;
        else {
            let currentNode: HashNode<T> | null = this._bucketList[index];
            while (currentNode!.next) {
                if (currentNode!.next.key === key) {
                    currentNode!.next.value = value;
                    return;
                }
                currentNode = currentNode!.next;
            }
            currentNode!.next = new HashNode<T>(key, value);
        }
    }

    public fetch = (key: string): T | null => {
        const index: number = this.hash(key);
        let currentNode: HashNode<T> | null = this._bucketList[index];
        while (currentNode) {
            if (currentNode.key === key) return currentNode.value;
            currentNode = currentNode.next;
        }
        return null;
    }

    public delete = (key: string): boolean => {
        const index: number = this.hash(key);
        if (!this._bucketList[index]) return false;
        else if (this._bucketList[index]!.key === key) {
            this._bucketList[index] = this._bucketList[index]!.next;
            return true;
        }
        else {
            let currentNode: HashNode<T> | null = this._bucketList[index];
            while (currentNode!.next) {
                if (currentNode!.next.key === key) {
                    currentNode!.next = currentNode!.next.next;
                    return true;
                }
                currentNode = currentNode!.next;
            }
            return false;
        }
    }
}