innerWidth.js

/**
 * This method returns an element's width including `padding`, which is excluded from `el.offsetWidth`.
 * 
 * @param {Element} element - An Element
 * @returns {number} Integer
 */
export default function innerWidth (el) {
    var style = getComputedStyle(el);
    return el.offsetWidth - parseInt(style.paddingLeft) - parseInt(style.paddingRight);
}