/**
 * check if element is within the viewport
 * https://gist.github.com/davidtheclark/5515733#gistcomment-2113205
 *
 * Please update `isElementClickable.js` if the script is updated!
 * @param  {HTMLElement} elem  element to check
 * @return {Boolean}           true if element is within viewport
 */
export default function isElementInViewport (elem: HTMLElement) {
    if (!elem.getBoundingClientRect) {
        return false
    }

    const rect = elem.getBoundingClientRect()

    const windowHeight = (window.innerHeight || document.documentElement.clientHeight)
    const windowWidth = (window.innerWidth || document.documentElement.clientWidth)

    const vertInView = (rect.top <= windowHeight) && ((rect.top + rect.height) > 0)
    const horInView = (rect.left <= windowWidth) && ((rect.left + rect.width) > 0)

    return (vertInView && horInView)
}