How to use functions like ease in out in pure js?

Question

JavaScript

There is progress, which changes from 0 to 1, depending on this, the width of the element changes.
I want to make an animation using ease in out.

Now like this:

// 250 final width
let width = Math.round(e.progress.toFixed(2) * 250);

Answer 1

Use the link that was given to you in the comments https://learn.javascript.ru/js-animation
Or, just specify this animation through css. and through js you change the value of the width or other properties. In my opinion, this is much easier than bothering and writing them in js.
transition: .2s ease-in-out;