ListNode in TypeScript (a generic example)

ListNode.ts

export class ListNode<T> {
    val: T;
    next: ListNode<T> | null;

    constructor(val: T, next: ListNode<T> | null = null) {
        this.val = val;
        this.next = next;
    }

    /**
     * make next of this to be `left`
     * @param left 
     */
    beNextOf(left: ListNode<T>) {
        left.next = this;
        return left;
    }

    /**
     * create a `ListNode` from an array
     * @param arr 
     */
    static fromArray<ItemType>(arr: ItemType[]) {
        const nodes = arr.map(item => new ListNode(item));

        return nodes.reduceRight((acc, cur) => {
            return acc.beNextOf(cur);
        });
    }

    /**
     * forEach a `ListNode`
     * @param cb 
     */
    forEach(cb: (item: T, idx: number) => void, idx = 0) {
        cb(this.val, idx);
        // recursive exec this.forEach when this.next is not null 
        this.next && this.next.forEach(cb, idx + 1);
    }
}

// create a ListNode from an array
const n = ListNode.fromArray([1, 2, 3, 4]);

// forEach
n.forEach((val, idx) => {
    console.log('val', val, 'idx', idx);
});