Iterator pattern

iterator-pattern.ts

export interface Iterator<T> {
	next(): T;
	hasNext(): boolean;
}

export interface Aggregator<T> {
	createIterator(): Iterator<T>;
}

export class ConcreteIterator<IteratorType> implements Iterator<IteratorType> {
	private collection: IteratorType[] = [];
	private position: number = 0;

	constructor(collection: IteratorType[]) {
		this.collection = collection;
	}

	public next(): IteratorType {
        if(this.position < this.collection.length){
            var result = this.collection[this.position];
            this.position += 1;
            return result;
        } else {
            return null;
        }
	}

	public hasNext(): boolean {
		return this.position < this.collection.length;
	}
}

export class Numbers implements Aggregator<number> {
	private collection: number[] = [];

	constructor(collection: number[]) {
		this.collection = collection;
	}
	public createIterator(): Iterator<number> {
		return new ConcreteIterator(this.collection);
	}
}

class Employee {
    public id: number;
    public name: string
}

export class Employees implements Aggregator<Employee> {
    private employees: Employee[];

    constructor(employees: Employee[]) {
        this.employees = employees;
	}

    createIterator(): Iterator<Employee> {
        return new ConcreteIterator(this.employees);
    }
}

const list: Employee[] = [
    {id: 1, name: 'Milad'},
    {id: 2, name: 'Alexandra'}
];

const employees = new Employees(list);
const iterator = employees.createIterator();

console.log(iterator.next().name); // { id: 1, name: 'Milad' }
console.log(iterator.next()); // { id: 2, name: 'Alexandra' }
console.log(iterator.next()); // null
console.log(iterator.next()); // null
console.log(iterator.next()); // null
console.log(iterator.next()); // null
console.log(iterator.next()); // null