In this article, we will learn how to use and implement the Iterator Pattern in TypeScript with an example.

Iterator is a behavioral design pattern that lets you traverse elements of a collection without exposing its underlying representation (list, stack, tree, etc.).

TypeScript Iterator Pattern Example

Let's create iterator.ts file and add the following code to it:

export interface Iterator {

    next(): any;
    hasNext(): boolean;
}

export interface Aggregator {
    createIterator(): Iterator;
}

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

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

    public next(): any {
        // Error handling is left out
        var result = this.collection[this.position];
        this.position += 1;
        return result;
    }

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

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

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

Usage

Let's create demo.ts file and add the following code to it:

import { ConcreteIterator, Numbers } from "./iterator";

export function show() : void {
 var nArray = [1, 7, 21, 657, 3, 2, 765, 13, 65],
  numbers: Numbers = new Numbers(nArray),
  it: ConcreteIterator = <ConcreteIterator>numbers.createIterator();

 while (it.hasNext()) {
  console.log(it.next());
 }

}
show();

Run:

• Compile the above code using the TypeScript compiler.
• Above code is compiled to plan JavaScript code
• Run Javascript code using node

design_patterns_in_typescript\iterator> tsc --target ES5 .\demo.ts
design_patterns_in_typescript\iterator> node .\demo.js
1
7
21
657
3
2
765
13
65

All TypeScript Design Patterns

1. Creational Design Patterns

Creational patterns provide various object creation mechanisms, which increase flexibility and reuse of existing code.

1. TypeScript Singleton Pattern Example
2. TypeScript Factory Design Pattern with Example
3. TypeScript Abstract Factory Pattern Example
4. TypeScript Builder Pattern Example
5. TypeScript Prototype Pattern Example

2. Structural Design Patterns

Structural patterns explain how to assemble objects and classes into larger structures while keeping these structures flexible and efficient.

1. TypeScript Bridge Pattern Example
2. TypeScript Adapter Pattern Example
3. TypeScript Decorator Pattern Example
4. TypeScript Composite Pattern Example
5. TypeScript Flyweight Design Pattern Example
6. TypeScript Facade Pattern Example
7. TypeScript Proxy Pattern Example

3. Behavioral Design Patterns

Behavioral design patterns are concerned with algorithms and the assignment of responsibilities between objects.

1. TypeScript Command Pattern Example
2. TypeScript Chain of Responsibility Pattern Example
3. TypeScript Visitor Pattern Example
4. TypeScript Template Method Pattern Example
5. TypeScript Strategy Pattern Example
6. TypeScript State Pattern Example
7. TypeScript Observer Pattern Example
8. TypeScript Memento Pattern Example
9. TypeScript Mediator Pattern Example
10. TypeScript Iterator Pattern Example
11. TypeScript Interpreter Design Pattern Example