how to get the width by size in javascript code example

Example 1: get screen width javascript

window.screen.width
//or just
screen.width

Example 2: get width of a dom element js

// Get Content + Padding + Border
let box = document.querySelector('div');
let width = box.offsetWidth;
let height = box.offsetHeight;

// Get Content + Padding only
let box = document.querySelector('div');
let width = box.clientWidth;
let height = box.clientHeight;