How do I use a for-in loop in JavaScript?

How do I use a for-in loop in JavaScript?

A for-in loop is used to iterate over the properties of an object. Here's the syntax: for (let key in object) { ... }.

Can you give me an example of using a for-in loop?

Sure! Here's an example:

const person = { name: 'Alice', age: 25, city: 'New York' };
for (let key in person) {
    console.log(key + ': ' + person[key]);
}

What if I want to use it with an array?

You can use a for-in loop with arrays, but it's not recommended. Use a for-of loop instead for better performance.

Why is for-in not recommended for arrays?

For-in loops iterate over all enumerable properties, which can include inherited properties. This can lead to unexpected results with arrays.