JavaScript: Ways to create array of given length

How do you create an array in JavaScript and fill it with a constant? The most naive way would be:

const length = 10;
const arr = [];
for (let i = 0; i < length; i++ ) {
    arr.push(1);
}

But that seems too much work for such a simple task.

Dr. Axel Rauschmayer in his blog discussed this problem. He gave some very interesting ways to accomplish this task. The original post was written in 2013. Since then, JavaScript has evolved a lot. This blog will discuss some other ways.

Array.prototype.fill

This might be the easiest way to initialize an array with value. ES 6 provides fill method. So you can do:

new Array(3).fill('a') // ['a', 'a', 'a']

At the time of writing. All major browsers except IE supports this.

Array.from

I saw Ben Lesh used this in one of his workshop and I think it's pretty cool. From MDN,

The Array.from() method creates a new Array instance from an array-like or iterable object.

Well, what's Array-like?

In fact, it could be an just an Object with a length attribute. For example

Array.from({length: 3}); // [ undefined, undefined, undefined ]

With that we can initialize our array with map

Array.from({length: 3}).map(() => 'a');