HTML implementation to obtain the width and height of the browser's visible area (pure code)

/**
     * 获取浏览器可视区域宽度
     */
    function getViewPortOffset() {
        if (window.innerWidth) {
            return {
                w: window.innerWidth,
                h: window.innerHeight
            }
        } else if (document.compatMode = "BackCompat") {
            return {
                w: document.body.clientWidth,
                h: document.body.clientHeigth
            }
        } else {
            return {
                w: document.documentElement.clientWidth,
                h: document.documentElement.clientHeight
            }
        }
    }
    console.log(getViewPortOffset());