How do I use Symbol.iterator in JavaScript?

How do I use Symbol.iterator in JavaScript?

The Symbol.iterator is a built-in symbol that specifies the default iterator for an object. You can define it in your custom objects to make them iterable.

Can you show me an example of how to implement it?

Sure! Here's a simple example:

class MyCollection {
    constructor() {
        this.items = [];
    }
    add(item) {
        this.items.push(item);
    }
    [Symbol.iterator]() {
        let index = 0;
        return {
            next: () => {
                if (index < this.items.length) {
                    return { value: this.items[index++], done: false };
                } else {
                    return { done: true };
                }
            }
        };
    }
}

const collection = new MyCollection();
collection.add('item1');
collection.add('item2');

for (const item of collection) {
    console.log(item);
}

What does the next method do in this context?

The next method returns an object with two properties: value, which is the current item, and done, which indicates if the iteration is complete.

Can I use Symbol.iterator with built-in data structures?

Yes, built-in data structures like Arrays, Maps, and Sets already implement Symbol.iterator, allowing you to iterate over them directly.