JAVASCRIPT FOR IN LOOP

JavaScript for in loop is used to loop through properties of an object.

For In Loop Syntax:

for (key in object) { //can also be variable in array
  // code 
}

Usage on a sample JavaScript object

const car = { company: "Toyota", model: "Corolla", year: 2021 };
 
let text = "";
for (let x in car) {
  text += car[x] + " ";
}

In this example, the car object is iterated over in the for in loop. A key is returned in each iteration which is used to access the value of the key. The value of the key is car[x].

They for in loop can also be applied to arrays.

const cars = ["Corolla", "Bugatti", "Tesla"];

let text = "";
for (let x in cars) {
  text += cars[x] + " ";
}