The for…in statement loops over the properties of an object, executing a block of code inside the loop once for each item found.

<!-- html element to place output -->
<p id="my_output"></p>

The following loops through the array and outputs each item found, ending the loop after finding the final item.

// variables
let my_cars = ['Lamborghini', 'Ferrari', 'Maserati', 'Alfa Romeo'];
let text = '';

// loop
for (let x in my_cars) {
    text += my_cars[x] + " ";
}

// output to HTML element
document.getElementById('my_output').innerHTML = text;

Lamborghini Ferrari Maserati Alfa Romeo

for (x in object) {
    code to be executed
}