[TOC] ## 概述 ``` a = 1; window.a // 1 ``` ## window.getSelection() 返回用户选中的文字 ``` var selObj = window.getSelection(); var selectedText = selObj.toString(); ``` ## window.requestAnimationFrame() 下次重绘时候执行 推迟到浏览器下一次重流时执行,重绘通常是 16ms 执行一次. 某个函数会改变网页的布局，一般就放在`window.requestAnimationFrame()`里面执行 `window.requestAnimationFrame(callback) ` 格式: ``` function demo() { //code window.requestAnimationFrame(demo) } window.requestAnimationFrame(demo) ``` demo: ``` // 重绘代价高 function doubleHeight(element) { var currentHeight = element.clientHeight; element.style.height = (currentHeight * 2) + 'px'; } all_my_elements.forEach(doubleHeight); // 重绘代价低 function doubleHeight(element) { var currentHeight = element.clientHeight; window.requestAnimationFrame(function () { element.style.height = (currentHeight * 2) + 'px'; }); } all_my_elements.forEach(doubleHeight); ``` ## window.requestIdleCallback() 推迟到系统空闲执行