[TOC] ## 概述 ``` a = 1; window.a // 1 ``` ## window.getSelection() 返回用戶選中的文字 ``` var selObj = window.getSelection(); var selectedText = selObj.toString(); ``` ## window.requestAnimationFrame() 下次重繪時候執行 推遲到瀏覽器下一次重流時執行,重繪通常是 16ms 執行一次. 某個函數會改變網頁的布局，一般就放在`window.requestAnimationFrame()`里面執行 `window.requestAnimationFrame(callback) ` 格式: ``` function demo() { //code window.requestAnimationFrame(demo) } window.requestAnimationFrame(demo) ``` demo: ``` // 重繪代價高 function doubleHeight(element) { var currentHeight = element.clientHeight; element.style.height = (currentHeight * 2) + 'px'; } all_my_elements.forEach(doubleHeight); // 重繪代價低 function doubleHeight(element) { var currentHeight = element.clientHeight; window.requestAnimationFrame(function () { element.style.height = (currentHeight * 2) + 'px'; }); } all_my_elements.forEach(doubleHeight); ``` ## window.requestIdleCallback() 推遲到系統空閑執行