clientHeight = height + paddingHeight 可見高度
offsetHeight = clientHeight + border
scrollHeight = contentHeight + paddingHeight 內(nèi)容高度
scrollTop 向下滾動(dòng)的距離
-
scrollHeight >= clientHeight,當(dāng)內(nèi)容高度小于可見高度時(shí),scrollHeight為clientHeight - 當(dāng)滾動(dòng)至最底端時(shí),
scrollHeight === clientHeight + scrollTop