8. DOM操作は同期的処理で非効率である Layout thrashing var h1 = element1.clientHeight; <== Read element1.style.height = (h1 * 2) + 'px'; <== Write var h2 = element2.clientHeight; <== Read(trigger layout) element2.style.height = (h1 * 2) + 'px'; <== Write var h3 = element3.clientHeight; <== Read(trigger layout) element3.style.height = (h3 * 2) + 'px'; <== Write var h1 = element1.clientHeight; <== Read var h2 = ele