一、效果图（如下）及使用的技术
实现用sass实现页面中右侧固定侧边栏的样式，用require.js实现返回顶部的功能
二、sass
具体的sass的介绍就不多说了，大家可以参考sass官网介绍，下面说一下sass的两种编译方法；
a、koala编译
koala 是一款桌面程序，支持 less 、 sass 、 coffeescript 即时编译。下载地址：http://koala-app.com/
koala可以直接对scss进行编译，不需要敲命令，并且可以对scss进行监控，具体使用方法见：http://www.w3cplus.com/preprocessor/sass-gui-tool-koala.html
注：此种编译方法比较方便，只要下载koalo即可，新建*.scss文件，拖进工作区点击”完成“，即可，并且可以监控添加到工作区的文件，不用每次点击编译；
b、sass命令编译（推荐）
此方法需要进行以下步骤：
（1）因为sass依赖于ruby环境，所以装sass之前先确认装了ruby。官网下载：ruby；
在安装的时候，请勾选Add Ruby executables to your PATH这个选项，添加环境变量，不然以后使用编译软件的时候会提示找不到ruby环境
（2）安装完ruby之后，在开始菜单中，找到刚才我们安装的ruby，打开Start Command Prompt with Ruby
然后在命令行中直接输入：
<span style="color: #008080;"> gem install sass</span>
按回车安装，如果安装不成功，可以直接在http://www.w3cplus.com/sassguide/install.html 中下载图中的“sass安装文件”
下载之后放到ruby的安装目录下的gems文件夹中即可（如下图）
安装完成后可以在命令行中输入命令：
* 查看sass版本的命令行为
sass -v
* 你也可以运行帮助命令行来查看你需要的命令
sass -h
* 单文件转换命令
sass style.scss style.css
* 单文件监听命令
sass --watch style.scss:style.css
* 文件夹监听命令
sass --watch sassFileDirectory:cssFileDirectory
三、require.js使用基础
新建一个目录，结构如下
目录toolbar下有index.html、jquery-1.11.3js、main.js、require.js。require.js和jquery-1.11.3.js去各自官网下载即可。
index.html如下：
<span style="color: #008080;"> 1</span> <span style="color: #0000ff;"><span style="color: #ff00ff;">doctype html</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 2</span> <span style="color: #0000ff;"><span style="color: #800000;">html</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 3</span> <span style="color: #0000ff;"><span style="color: #800000;">head</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 4</span> <span style="color: #0000ff;"><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>requirejs<span style="color: #0000ff;"></span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 5</span> <span style="color: #0000ff;"><span style="color: #800000;">meta </span><span style="color: #ff0000;">charset</span><span style="color: #0000ff;">="utf-8"</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 6</span> <span style="color: #0000ff;"><span style="color: #800000;">script </span><span style="color: #ff0000;">data-main</span><span style="color: #0000ff;">="js/main"</span><span style="color: #ff0000;"> src</span><span style="color: #0000ff;">="js/require.js"</span><span style="color: #0000ff;">></span><span style="color: #800000;">script</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 7</span> <span style="color: #0000ff;"></span><span style="color: #800000;">head</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 8</span> <span style="color: #0000ff;"><span style="color: #800000;">body</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 9</span> <span style="color: #008080;">10</span> <span style="color: #0000ff;"></span><span style="color: #800000;">body</span><span style="color: #0000ff;">></span> <span style="color: #008080;">11</span> <span style="color: #0000ff;"></span><span style="color: #800000;">html</span><span style="color: #0000ff;">></span> <span style="color: #008080;">12</span> </span></span></span></span></span></span></span>
使用requirejs很简单，只需要在head中通过script标签引入它（实际上除了require.js，其它文件模块都不再使用script标签引入）。
细心的同学会发现script标签上了多了一个自定义属性：data-main="main"，等号右边的main指的main.js。当然可以使用任意的名称。
这个main指主模块或入口模块，好比c或java的主函数main。
main.js如下
<span style="color: #008080;">1</span> <span style="color: #000000;">require.config({
</span><span style="color: #008080;">2</span> <span style="color: #000000;"> paths: {
</span><span style="color: #008080;">3</span> jquery: 'jquery-1.11.3'<span style="color: #008000;">//</span><span style="color: #008000;">此处用不用添加.js后缀，否则执行的时候会报错</span>
<span style="color: #008080;">4</span> <span style="color: #000000;"> }
</span><span style="color: #008080;">5</span> <span style="color: #000000;">});
</span><span style="color: #008080;">6</span>
<span style="color: #008080;">7</span> require(['jquery'], <span style="color: #0000ff;">function</span><span style="color: #000000;">($) {
</span><span style="color: #008080;">8</span> <span style="color: #000000;"> alert($().jquery);
</span><span style="color: #008080;">9</span> });
main.js中就两个函数调用require.config和require。
require.config用来配置一些参数，它将影响到requirejs库的一些行为。
require.config的参数是一个JS对象，常用的配置有baseUrl，paths等。
这里配置了paths参数，使用模块名“jquery”，其实际文件路径jquery-1.11.3.js（后缀.js可以省略）。
注：有些同学习惯用npm 来下载相关文件，在这里有一点需要注意的是：
下载require.js的命令是：
npm install requirejs
而不是( 注 意 )
npm install require.js
四、功能实现
项目目录结构如下：
在命令行输入命令如下，对scss文件夹进行监听并将scss中的scss文件编译到css文件夹中；
1、html部分：
<span style="color: #008080;"> 1</span> <span style="color: #0000ff;"><span style="color: #ff00ff;">DOCTYPE html</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 2</span> <span style="color: #0000ff;"><span style="color: #800000;">html </span><span style="color: #ff0000;">lang</span><span style="color: #0000ff;">="en"</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 3</span> <span style="color: #0000ff;"><span style="color: #800000;">head</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 4</span> <span style="color: #0000ff;"><span style="color: #800000;">meta </span><span style="color: #ff0000;">charset</span><span style="color: #0000ff;">="UTF-8"</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 5</span> <span style="color: #0000ff;"><span style="color: #800000;">title</span><span style="color: #0000ff;">></span>toolbar<span style="color: #0000ff;"></span><span style="color: #800000;">title</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 6</span> <span style="color: #0000ff;"><span style="color: #800000;">link </span><span style="color: #ff0000;">rel</span><span style="color: #0000ff;">="stylesheet"</span><span style="color: #ff0000;"> href</span><span style="color: #0000ff;">="css/index.css"</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 7</span> <span style="color: #008080;"> 8</span> <span style="color: #0000ff;"></span><span style="color: #800000;">head</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 9</span> <span style="color: #0000ff;"><span style="color: #800000;">body</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 10</span> <span style="color: #0000ff;"><span style="color: #800000;">div </span><span style="color: #ff0000;">class</span><span style="color: #0000ff;">="toolbar"</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 11</span> <span style="color: #0000ff;"><span style="color: #800000;">a </span><span style="color: #ff0000;">href</span><span style="color: #0000ff;">="javascript:;"</span><span style="color: #ff0000;"> class</span><span style="color: #0000ff;">="toolbar-item toolbar-item-weixin"</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 12</span> <span style="color: #0000ff;"><span style="color: #800000;">span </span><span style="color: #ff0000;">class</span><span style="color: #0000ff;">="toolbar-layout"</span><span style="color: #0000ff;">></span><span style="color: #800000;">span</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 13</span> <span style="color: #0000ff;"></span><span style="color: #800000;">a</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 14</span> <span style="color: #0000ff;"><span style="color: #800000;">a </span><span style="color: #ff0000;">href</span><span style="color: #0000ff;">="javascript:;"</span><span style="color: #ff0000;"> class</span><span style="color: #0000ff;">="toolbar-item toolbar-item-feedback"</span><span style="color: #0000ff;">></span><span style="color: #800000;">a</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 15</span> <span style="color: #0000ff;"><span style="color: #800000;">a </span><span style="color: #ff0000;">href</span><span style="color: #0000ff;">="javascript:;"</span><span style="color: #ff0000;"> class</span><span style="color: #0000ff;">="toolbar-item toolbar-item-app"</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 16</span> <span style="color: #0000ff;"><span style="color: #800000;">span </span><span style="color: #ff0000;">class</span><span style="color: #0000ff;">="toolbar-layout"</span><span style="color: #0000ff;">></span><span style="color: #800000;">span</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 17</span> <span style="color: #0000ff;"></span><span style="color: #800000;">a</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 18</span> <span style="color: #0000ff;"><span style="color: #800000;">a </span><span style="color: #ff0000;">id</span><span style="color: #0000ff;">="backTop"</span><span style="color: #ff0000;"> href</span><span style="color: #0000ff;">="javascript:;"</span><span style="color: #ff0000;"> class</span><span style="color: #0000ff;">="toolbar-item toolbar-item-top"</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 19</span> <span style="color: #0000ff;"><span style="color: #800000;">span </span><span style="color: #ff0000;">class</span><span style="color: #0000ff;">="toolbar-btn"</span><span style="color: #0000ff;">></span><span style="color: #800000;">span</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 20</span> <span style="color: #0000ff;"></span><span style="color: #800000;">a</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 21</span> <span style="color: #0000ff;"></span><span style="color: #800000;">div</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 22</span> <span style="color: #008000;"><!--</span><span style="color: #008000;">下面部分是为了使页面出现滚动条，方便测试</span><span style="color: #008000;">--></span> <span style="color: #008080;"> 23</span> <span style="color: #0000ff;"><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>测试<span style="color: #0000ff;"></span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 24</span> <span style="color: #0000ff;"><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>测试<span style="color: #0000ff;"></span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 25</span> <span style="color: #0000ff;"><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>测试<span style="color: #0000ff;"></span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> 26</span> <span style="color: #0000ff;"><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>测试<span style="color: #0000ff;"></span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span> <span style="color: #008080;"> ...</span> <span style="color: #008080;">119</span> <span style="color: #0000ff;"><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>测试<span style="color: #0000ff;"></span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span> <span style="color: #008080;">120</span> <span style="color: #0000ff;"><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>测试<span style="color: #0000ff;"></span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span> <span style="color: #008080;">121</span> <span style="color: #0000ff;"><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>测试<span style="color: #0000ff;"></span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span> <span style="color: #008080;">122</span> <span style="color: #0000ff;"><span style="color: #800000;">p</span><span style="color: #0000ff;">></span>测试<span style="color: #0000ff;"></span><span style="color: #800000;">p</span><span style="color: #0000ff;">></span> <span style="color: #008080;">123</span> <span style="color: #0000ff;"><span style="color: #800000;">script </span><span style="color: #ff0000;">src</span><span style="color: #0000ff;">="js/require.js"</span><span style="color: #ff0000;"> data-main</span><span style="color: #0000ff;">="js/main"</span><span style="color: #0000ff;">></span><span style="color: #800000;">script</span><span style="color: #0000ff;">></span> <span style="color: #008080;">124</span> <span style="color: #0000ff;"></span><span style="color: #800000;">body</span><span style="color: #0000ff;">></span> <span style="color: #008080;">125</span> <span style="color: #0000ff;"></span><span style="color: #800000;">html</span><span style="color: #0000ff;">></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>
2、css & scss部分：
scss文件夹中的：
(1) _mixin.scss: scss可以像js一样，将一些公共的样式封装成函数，便于重复利用
<span style="color: #008080;"> 1</span> <span style="color: #800000;">@mixin opacity($opacity)</span>{
<span style="color: #008080;"> 2</span> <span style="color: #ff0000;"> opacity</span>:<span style="color: #0000ff;"> $opacity</span>;
<span style="color: #008080;"> 3</span> <span style="color: #ff0000;"> filter</span>:<span style="color: #0000ff;"> opacity($opacity * 100)</span>;
<span style="color: #008080;"> 4</span> }
<span style="color: #008080;"> 5</span> <span style="color: #800000;">@mixin transform-origin ($transform-origin)</span>{
<span style="color: #008080;"> 6</span> <span style="color: #ff0000;"> transform-origin</span>:<span style="color: #0000ff;"> $transform-origin</span>;
<span style="color: #008080;"> 7</span> <span style="color: #ff0000;"> -webkit-transform-origin</span>:<span style="color: #0000ff;"> $transform-origin</span>;
<span style="color: #008080;"> 8</span> <span style="color: #ff0000;"> -o-transform-origin</span>:<span style="color: #0000ff;"> $transform-origin</span>;
<span style="color: #008080;"> 9</span> <span style="color: #ff0000;"> -ms-transform-origin</span>:<span style="color: #0000ff;"> $transform-origin</span>;
<span style="color: #008080;">10</span> <span style="color: #ff0000;"> -moz-transform-origin</span>:<span style="color: #0000ff;"> $transform-origin</span>;
<span style="color: #008080;">11</span> }
<span style="color: #008080;">12</span> <span style="color: #800000;">@mixin scale($scale)</span>{
<span style="color: #008080;">13</span> <span style="color: #ff0000;"> transform</span>:<span style="color: #0000ff;"> scale($scale)</span>;
<span style="color: #008080;">14</span> <span style="color: #ff0000;"> -webkit-transform</span>:<span style="color: #0000ff;"> scale($scale)</span>;
<span style="color: #008080;">15</span> <span style="color: #ff0000;"> -o-transform</span>:<span style="color: #0000ff;"> scale($scale)</span>;
<span style="color: #008080;">16</span> <span style="color: #ff0000;"> -ms-transform</span>:<span style="color: #0000ff;"> scale($scale)</span>;
<span style="color: #008080;">17</span> <span style="color: #ff0000;"> -moz-transform</span>:<span style="color: #0000ff;"> scale($scale)</span>;
<span style="color: #008080;">18</span> }
<span style="color: #008080;">19</span> <span style="color: #800000;">@mixin transition($transition)</span>{
<span style="color: #008080;">20</span> <span style="color: #ff0000;"> transition</span>:<span style="color: #0000ff;"> $transition</span>;
<span style="color: #008080;">21</span> <span style="color: #ff0000;"> -webkit-transition</span>:<span style="color: #0000ff;"> $transition</span>;
<span style="color: #008080;">22</span> <span style="color: #ff0000;"> -o-transition</span>:<span style="color: #0000ff;"> $transition</span>;
<span style="color: #008080;">23</span> <span style="color: #ff0000;"> -ms-transition</span>:<span style="color: #0000ff;"> $transition</span>;
<span style="color: #008080;">24</span> <span style="color: #ff0000;"> -moz-transition</span>:<span style="color: #0000ff;"> $transition</span>;
<span style="color: #008080;">25</span> }(2) toobar.scss : 该模块中的自有样式（只在自个模块中使用的）
<span style="color: #008080;"> 1</span> <span style="color: #800000;">@import "mixin";
</span><span style="color: #008080;"> 2</span> <span style="color: #800000;">@mixin toolbar-item($pos,$hoverPos)</span>{
<span style="color: #008080;"> 3</span> <span style="color: #ff0000;"> background-position</span>:<span style="color: #0000ff;"> 0 $pos</span>;
<span style="color: #008080;"> 4</span> <span style="color: #ff0000;"> &</span>:<span style="color: #0000ff;">hover {
</span><span style="color: #008080;"> 5</span> <span style="color: #0000ff;"> background-position: 0 $hoverPos</span>;
<span style="color: #008080;"> 6</span> }
<span style="color: #008080;"> 7</span>
<span style="color: #008080;"> 8</span> <span style="color: #800000;">}
</span><span style="color: #008080;"> 9</span> <span style="color: #800000;">$toolbar-size: 52px;
</span><span style="color: #008080;">10</span>
<span style="color: #008080;">11</span> <span style="color: #800000;">.toolbar-item, .toolbar-layout </span>{
<span style="color: #008080;">12</span> <span style="color: #ff0000;"> background-image</span>:<span style="color: #0000ff;"> url(../img/toolbar.png)</span>;
<span style="color: #008080;">13</span> <span style="color: #ff0000;"> background-repeat</span>:<span style="color: #0000ff;"> no-repeat</span>;
<span style="color: #008080;">14</span> }
<span style="color: #008080;">15</span> <span style="color: #800000;">.toolbar </span>{
<span style="color: #008080;">16</span> <span style="color: #ff0000;"> position</span>:<span style="color: #0000ff;"> fixed</span>;
<span style="color: #008080;">17</span> <span style="color: #ff0000;"> left</span>:<span style="color: #0000ff;"> 50%</span>;
<span style="color: #008080;">18</span> <span style="color: #ff0000;"> bottom</span>:<span style="color: #0000ff;"> 100px</span>;
<span style="color: #008080;">19</span> <span style="color: #ff0000;"> margin-left</span>:<span style="color: #0000ff;"> -$toolbar-size / 2</span>;
<span style="color: #008080;">20</span> }
<span style="color: #008080;">21</span> <span style="color: #800000;">.toolbar-item </span>{
<span style="color: #008080;">22</span> <span style="color: #ff0000;"> position</span>:<span style="color: #0000ff;"> relative</span>;
<span style="color: #008080;">23</span> <span style="color: #ff0000;"> display</span>:<span style="color: #0000ff;"> block</span>;
<span style="color: #008080;">24</span> <span style="color: #ff0000;"> width</span>:<span style="color: #0000ff;"> $toolbar-size</span>;
<span style="color: #008080;">25</span> <span style="color: #ff0000;"> height</span>:<span style="color: #0000ff;"> $toolbar-size</span>;
<span style="color: #008080;">26</span> <span style="color: #ff0000;"> margin-top</span>:<span style="color: #0000ff;"> 1px</span>;
<span style="color: #008080;">27</span>
<span style="color: #008080;">28</span> <span style="color: #ff0000;"> @include transition(background-position 1s);
</span><span style="color: #008080;">29</span> <span style="color: #ff0000;"> &</span>:<span style="color: #0000ff;">hover {
</span><span style="color: #008080;">30</span> <span style="color: #0000ff;"> .toolbar-layout {
</span><span style="color: #008080;">31</span> <span style="color: #0000ff;"> @include opacity(1)</span>;
<span style="color: #008080;">32</span> <span style="color: #ff0000;"> @include scale(1);
</span><span style="color: #008080;">33</span> <span style="color: #ff0000;"> @include transition(all 1s);
</span><span style="color: #008080;">34</span> }
<span style="color: #008080;">35</span> <span style="color: #800000;"> }
</span><span style="color: #008080;">36</span>
<span style="color: #008080;">37</span> <span style="color: #800000;">}
</span><span style="color: #008080;">38</span> <span style="color: #800000;">.toolbar-layout </span>{
<span style="color: #008080;">39</span> <span style="color: #ff0000;"> position</span>:<span style="color: #0000ff;"> absolute</span>;
<span style="color: #008080;">40</span> <span style="color: #ff0000;"> right</span>:<span style="color: #0000ff;"> $toolbar-size - 5</span>;
<span style="color: #008080;">41</span> <span style="color: #ff0000;"> bottom</span>:<span style="color: #0000ff;"> 0</span>;
<span style="color: #008080;">42</span> <span style="color: #ff0000;"> width</span>:<span style="color: #0000ff;"> 172px</span>;
<span style="color: #008080;">43</span> <span style="color: #ff0000;"> @include transform-origin(95% 95%);
</span><span style="color: #008080;">44</span> <span style="color: #ff0000;"> @include opacity(0);
</span><span style="color: #008080;">45</span> <span style="color: #ff0000;"> @include scale(0.01);
</span><span style="color: #008080;">46</span> <span style="color: #ff0000;"> @include transition(all 1s);
</span><span style="color: #008080;">47</span>
<span style="color: #008080;">48</span> }
<span style="color: #008080;">49</span> <span style="color: #800000;">.toolbar-item-weixin </span>{
<span style="color: #008080;">50</span> <span style="color: #ff0000;"> @include toolbar-item(-798px, -860px);
</span><span style="color: #008080;">51</span>
<span style="color: #008080;">52</span> <span style="color: #ff0000;"> .toolbar-layout {
</span><span style="color: #008080;">53</span> <span style="color: #ff0000;"> height</span>:<span style="color: #0000ff;"> 212px</span>;
<span style="color: #008080;">54</span> <span style="color: #ff0000;"> background-position</span>:<span style="color: #0000ff;"> 0 0</span>;
<span style="color: #008080;">55</span> }
<span style="color: #008080;">56</span> <span style="color: #800000;">}
</span><span style="color: #008080;">57</span>
<span style="color: #008080;">58</span> <span style="color: #800000;">.toolbar-item-feedback </span>{
<span style="color: #008080;">59</span> <span style="color: #ff0000;"> @include toolbar-item(-426px,-488px);
</span><span style="color: #008080;">60</span>
<span style="color: #008080;">61</span> }
<span style="color: #008080;">62</span> <span style="color: #800000;">.toolbar-item-app </span>{
<span style="color: #008080;">63</span> <span style="color: #ff0000;"> @include toolbar-item(-550px,-612px);
</span><span style="color: #008080;">64</span>
<span style="color: #008080;">65</span> <span style="color: #ff0000;"> .toolbar-layout {
</span><span style="color: #008080;">66</span> <span style="color: #ff0000;"> height</span>:<span style="color: #0000ff;"> 194px</span>;
<span style="color: #008080;">67</span> <span style="color: #ff0000;"> background-position</span>:<span style="color: #0000ff;"> 0 -222</span>;
<span style="color: #008080;">68</span> }
<span style="color: #008080;">69</span> <span style="color: #800000;">}
</span><span style="color: #008080;">70</span> <span style="color: #800000;">.toolbar-item-top </span>{
<span style="color: #008080;">71</span> <span style="color: #ff0000;"> @include toolbar-item(-674px,-736px);
</span><span style="color: #008080;">72</span>
<span style="color: #008080;">73</span> }(3) index.scss: 该项目引入的样式文件，编译后为index.css，在html中只引入index.css，便于文件管理
<span style="color: #008080;">1</span> <span style="color: #800000;">@import "toolbar";</span>
3、js部分：
（1）jquery-1.11.3.js和require.js是该项目的依赖，可从各自官网下载，也可以通过npm下载，html中只引入require.js即可
（2）main.js是项目的入口文件
<span style="color: #000000;">require.config({
paths:{
jquery:</span>"./jquery-1.11.3"<span style="color: #000000;">
}
});
require([</span>'jquery',"backtop"],<span style="color: #0000ff;">function</span><span style="color: #000000;"> ($,backTop) {
</span><span style="color: #0000ff;">var</span> backTop = <span style="color: #0000ff;">new</span> backTop.BackTop($("#backTop"<span style="color: #000000;">),{//构造函数实例化
mode:</span>"move"<span style="color: #000000;">,
dest:</span>0<span style="color: #000000;">,
speed:</span>500<span style="color: #000000;">
});
});</span>
（3）backtop.js:
<span style="color: #008080;"> 1</span> define(["jquery","scrollTo"],<span style="color: #0000ff;">function</span><span style="color: #000000;">($,scrollTo){
</span><span style="color: #008080;"> 2</span>
<span style="color: #008080;"> 3</span> <span style="color: #0000ff;">function</span><span style="color: #000000;"> BackTop(el,opts){
</span><span style="color: #008080;"> 4</span>
<span style="color: #008080;"> 5</span> <span style="color: #0000ff;">this</span>.opts =<span style="color: #000000;"> $.extend({},BackTop.defaults,opts);
</span><span style="color: #008080;"> 6</span> <span style="color: #0000ff;">this</span>.$el =<span style="color: #000000;">$(el);
</span><span style="color: #008080;"> 7</span>
<span style="color: #008080;"> 8</span> <span style="color: #0000ff;">this</span>.scroll = <span style="color: #0000ff;">new</span><span style="color: #000000;"> scrollTo.ScrollTo({
</span><span style="color: #008080;"> 9</span> dest: 0<span style="color: #000000;">,
</span><span style="color: #008080;">10</span> speed:<span style="color: #0000ff;">this</span><span style="color: #000000;">.opts.speed
</span><span style="color: #008080;">11</span> <span style="color: #000000;"> });
</span><span style="color: #008080;">12</span>
<span style="color: #008080;">13</span> <span style="color: #0000ff;">if</span>(<span style="color: #0000ff;">this</span>.opts.mode === "move"<span style="color: #000000;">){
</span><span style="color: #008080;">14</span> <span style="color: #0000ff;">this</span>.$el.on("click", $.proxy(<span style="color: #0000ff;">this</span>._move,<span style="color: #0000ff;">this</span>));<span style="color: #008000;">//</span><span style="color: #008000;">改变this指向</span>
<span style="color: #008080;">15</span>
<span style="color: #008080;">16</span> }<span style="color: #0000ff;">else</span><span style="color: #000000;"> {
</span><span style="color: #008080;">17</span> <span style="color: #0000ff;">this</span>.$el.on("click", $.proxy(<span style="color: #0000ff;">this</span>._go,<span style="color: #0000ff;">this</span>));<span style="color: #008000;">//</span><span style="color: #008000;">改变this指向</span>
<span style="color: #008080;">18</span>
<span style="color: #008080;">19</span> <span style="color: #000000;"> }
</span><span style="color: #008080;">20</span>
<span style="color: #008080;">21</span> <span style="color: #0000ff;">this</span><span style="color: #000000;">._checkPosition();
</span><span style="color: #008080;">22</span> $(window).on("scroll",$.proxy(<span style="color: #0000ff;">this</span>._checkPosition,<span style="color: #0000ff;">this</span><span style="color: #000000;">));
</span><span style="color: #008080;">23</span>
<span style="color: #008080;">24</span> <span style="color: #000000;"> };
</span><span style="color: #008080;">25</span>
<span style="color: #008080;">26</span>
<span style="color: #008080;">27</span>
<span style="color: #008080;">28</span> BackTop.defaults =<span style="color: #000000;"> {
</span><span style="color: #008080;">29</span> mode:'move',<span style="color: #008000;">//</span><span style="color: #008000;">返回顶部的方式，直接返回还是动画返回</span>
<span style="color: #008080;">30</span> pos:$(window).height(),<span style="color: #008000;">//</span><span style="color: #008000;">返回顶部按钮显示隐藏的初始值</span>
<span style="color: #008080;">31</span> speed:800
<span style="color: #008080;">32</span> <span style="color: #000000;"> }
</span><span style="color: #008080;">33</span>
<span style="color: #008080;">34</span> BackTop.prototype._move = <span style="color: #0000ff;">function</span><span style="color: #000000;">(){
</span><span style="color: #008080;">35</span> <span style="color: #0000ff;">this</span><span style="color: #000000;">.scroll.move();
</span><span style="color: #008080;">36</span> <span style="color: #000000;"> }
</span><span style="color: #008080;">37</span> BackTop.prototype._go = <span style="color: #0000ff;">function</span><span style="color: #000000;">(){
</span><span style="color: #008080;">38</span> <span style="color: #0000ff;">this</span><span style="color: #000000;">.scroll.go();
</span><span style="color: #008080;">39</span> <span style="color: #000000;"> }
</span><span style="color: #008080;">40</span> BackTop.prototype._checkPosition = <span style="color: #0000ff;">function</span><span style="color: #000000;">(){
</span><span style="color: #008080;">41</span>
<span style="color: #008080;">42</span> <span style="color: #0000ff;">var</span> $el = <span style="color: #0000ff;">this</span><span style="color: #000000;">.$el;
</span><span style="color: #008080;">43</span>
<span style="color: #008080;">44</span> <span style="color: #0000ff;">if</span>($(window).scrollTop() > <span style="color: #0000ff;">this</span><span style="color: #000000;">.opts.pos){
</span><span style="color: #008080;">45</span>
<span style="color: #008080;">46</span> <span style="color: #000000;"> $el.fadeIn();
</span><span style="color: #008080;">47</span> }<span style="color: #0000ff;">else</span><span style="color: #000000;"> {
</span><span style="color: #008080;">48</span> <span style="color: #000000;"> $el.fadeOut();
</span><span style="color: #008080;">49</span> <span style="color: #000000;"> }
</span><span style="color: #008080;">50</span> <span style="color: #000000;"> };
</span><span style="color: #008080;">51</span>
<span style="color: #008080;">52</span> <span style="color: #0000ff;">return</span><span style="color: #000000;"> {BackTop:BackTop}
</span><span style="color: #008080;">53</span>
<span style="color: #008080;">54</span> });（4）scrollTo.js
<span style="color: #008080;"> 1</span> define(["jquery"],<span style="color: #0000ff;">function</span><span style="color: #000000;">($){
</span><span style="color: #008080;"> 2</span>
<span style="color: #008080;"> 3</span> <span style="color: #0000ff;">function</span><span style="color: #000000;"> ScrollTo(opts){
</span><span style="color: #008080;"> 4</span>
<span style="color: #008080;"> 5</span> <span style="color: #0000ff;">this</span>.opts =<span style="color: #000000;"> $.extend({},ScrollTo.defaults,opts);
</span><span style="color: #008080;"> 6</span>
<span style="color: #008080;"> 7</span> <span style="color: #0000ff;">this</span>.$el = $("html,body"<span style="color: #000000;">);
</span><span style="color: #008080;"> 8</span>
<span style="color: #008080;"> 9</span> <span style="color: #000000;"> };
</span><span style="color: #008080;">10</span>
<span style="color: #008080;">11</span> ScrollTo.prototype.move = <span style="color: #0000ff;">function</span><span style="color: #000000;">(){
</span><span style="color: #008080;">12</span> <span style="color: #0000ff;">var</span> opts = <span style="color: #0000ff;">this</span><span style="color: #000000;">.opts;
</span><span style="color: #008080;">13</span> <span style="color: #0000ff;">var</span> dest =<span style="color: #000000;"> opts.dest;
</span><span style="color: #008080;">14</span> <span style="color: #008000;">//</span><span style="color: #008000;">防止动画未结束多次执行动画</span>
<span style="color: #008080;">15</span> <span style="color: #0000ff;">if</span>($(window).scrollTop() != dest){<span style="color: #008000;">//</span><span style="color: #008000;">判断是否到达目的地</span>
<span style="color: #008080;">16</span>
<span style="color: #008080;">17</span> <span style="color: #0000ff;">if</span>(!<span style="color: #0000ff;">this</span>.$el.is(":animated")){<span style="color: #008000;">//</span><span style="color: #008000;">判断是否在运动</span>
<span style="color: #008080;">18</span>
<span style="color: #008080;">19</span> <span style="color: #0000ff;">this</span><span style="color: #000000;">.$el.animate({
</span><span style="color: #008080;">20</span> <span style="color: #000000;"> scrollTop:dest
</span><span style="color: #008080;">21</span> <span style="color: #000000;"> },opts.speed);
</span><span style="color: #008080;">22</span> <span style="color: #000000;"> }
</span><span style="color: #008080;">23</span> <span style="color: #000000;"> }
</span><span style="color: #008080;">24</span>
<span style="color: #008080;">25</span> <span style="color: #000000;"> };
</span><span style="color: #008080;">26</span> ScrollTo.prototype.go = <span style="color: #0000ff;">function</span><span style="color: #000000;">(){
</span><span style="color: #008080;">27</span>
<span style="color: #008080;">28</span> <span style="color: #0000ff;">var</span> dest = <span style="color: #0000ff;">this</span><span style="color: #000000;">.opts.dest;
</span><span style="color: #008080;">29</span>
<span style="color: #008080;">30</span> <span style="color: #0000ff;">if</span>($(window).scrollTop() !=<span style="color: #000000;"> dest){
</span><span style="color: #008080;">31</span> <span style="color: #0000ff;">this</span><span style="color: #000000;">.$el.scrollTop(dest);
</span><span style="color: #008080;">32</span> <span style="color: #000000;"> }
</span><span style="color: #008080;">33</span>
<span style="color: #008080;">34</span> <span style="color: #000000;"> };
</span><span style="color: #008080;">35</span> ScrollTo.defaults =<span style="color: #000000;"> {
</span><span style="color: #008080;">36</span> dest: 0,<span style="color: #008000;">//</span><span style="color: #008000;">目的地</span>
<span style="color: #008080;">37</span> speed:800<span style="color: #008000;">//</span><span style="color: #008000;">滚动速度</span>
<span style="color: #008080;">38</span> <span style="color: #000000;"> };
</span><span style="color: #008080;">39</span> <span style="color: #0000ff;">return</span><span style="color: #000000;"> {
</span><span style="color: #008080;">40</span> <span style="color: #000000;"> ScrollTo:ScrollTo
</span><span style="color: #008080;">41</span> <span style="color: #000000;"> }
</span><span style="color: #008080;">42</span> });
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