What is the difference between Symbol.iterator and Iterator in JavaScript?

What is the difference between Symbol.iterator and Iterator in JavaScript?

In JavaScript, Symbol.iterator is a built-in symbol that specifies the default iterator for an object, while an Iterator is an object that defines a sequence and potentially a return value upon completion.

Can you give me an example of how to use Symbol.iterator?

Sure! Here's a simple example:

const myArray = [1, 2, 3];
myArray[Symbol.iterator] = function() {
    let index = 0;
    return {
        next: () => {
            if (index < this.length) {
                return { value: this[index++], done: false };
            } else {
                return { done: true };
            }
        }
    };
};

for (const value of myArray) {
    console.log(value);
}

What happens if I don't implement Symbol.iterator?

If you don't implement Symbol.iterator, your object won't be iterable, meaning you can't use it in a for...of loop or with spread syntax. It will throw a TypeError.

Are there any built-in objects that use Symbol.iterator?

Yes, many built-in objects in JavaScript, like Arrays, Strings, and Maps, implement Symbol.iterator, allowing them to be easily iterated over.