Filling Objects via Loop in JavaScript

Objects can also be filled with data in loops. Let's look at an example. Suppose we have two arrays:

let keys = ['a', 'b', 'c', 'd', 'e'];
let values = [1, 2, 3, 4, 5];

Let's use them to create an object, taking the keys for this object from the first array, and the values - from the second one. To do this, let's run a loop and within the loop we will form our object:

let obj = {};

for (let i = 0; i <= 4; i++) {
	let key = keys[i];
	let value = values[i];
	
	obj[key] = value;
}

console.log(obj);

It is not necessary to introduce variables for the key and value, you can simply do it like this:

let obj = {};

for (let i = 0; i <= 4; i++) {
	obj[keys[i]] = values[i];
}

console.log(obj);

Given two arrays: the first with the names of the days of the week, and the second - with their serial numbers:

let arr1 = ['a', 'b', 'c', 'd', 'e'];
let arr2 = [1, 2, 3, 4, 5];

Using a loop, create an object whose keys will be the names of the days, and the values will be their numbers.

Given an object:

let obj = {a: 1, b: 2, c: 3, d: 4, e: 5};

Iterate over this object with a loop and write into a new object those elements which are even numbers.

Given an object:

let obj = {a: 1, b: 2, c: 3, d: 4, e: 5};

Iterate over this object with a loop and create a new object so that its keys become the elements of the old object, and the values become the keys of the old object.