js之展开收缩菜单，用到window.onload ,onclick,

目标效果：点击标签1，如果列表标签的style的display是block,改成none，否则改成block，来达到展开收缩菜单效果

一.准备阶段

html文件

 1 <!DOCTYPE html>
 2 <html lang="en">
 3 <head>
 4     <meta charset="UTF-8">
 5     <title>Title</title>
 6 </head>
 7 <body>
 8     <div id="box">
 9         <p id="btn">标签1</p>
10         <ul id="ull" style="display: block;">
11             <li><a href="#">手写</a></li>
12             <li><a href="#">拼音</a></li>
13         </ul>
14     </div>
15 </body>
16 </html>

运行后页面效果

二.：点击标签1隐藏列表

方法1

html代码

 1 <!DOCTYPE html>
 2 <html lang="en">
 3 <head>
 4     <meta charset="UTF-8">
 5     <title>Title</title>
 6 </head>
 7 <body>
 8     <div id="box">
 9         <p id="btn" onclick="document.getElementById('ull').style.display='none'">标签1</p>
10         <ul id="ull" style="display: block;">
11             <li><a href="#">手写</a></li>
12             <li><a href="#">拼音</a></li>
13         </ul>
14     </div>
15 </body>
16 </html>

效果从上图到下图

方法2

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        function tonone() {
            document.getElementById('ull').style.display='none';
        }
    </script>
</head>
<body>
    <div id="box">
        <p id="btn" onclick="tonone()">标签1</p>
        <ul id="ull" style="display: block;">
            <li><a href="#">手写</a></li>
            <li><a href="#">拼音</a></li>
        </ul>
    </div>
</body>
</html>

方法3

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        window.onload=function ()
        {
            document.getElementById('btn').onclick=function ()
            {
                document.getElementById('ull').style.display='none';
            }
        }
    </script>
</head>
<body>
    <div id="box">
        <p id="btn" >标签1</p>
        <ul id="ull" style="display: block;">
            <li><a href="#">手写</a></li>
            <li><a href="#">拼音</a></li>
        </ul>
    </div>
</body>
</html>

方法4

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        window.onload=function ()
        {
            var obtn = document.getElementById('btn');
            var oull = document.getElementById('ull');
            obtn.onclick=function ()
            {
                oull.style.display='none';
            }
        }
    </script>
</head>
<body>
    <div id="box">
        <p id="btn" >标签1</p>
        <ul id="ull" style="display: block;">
            <li><a href="#">手写</a></li>
            <li><a href="#">拼音</a></li>
        </ul>
    </div>
</body>
</html>

在方法4基础上加上if判断就可以实现页面展开收缩菜单功能

代码如下

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        window.onload=function ()
        {
            var obtn = document.getElementById('btn');
            var oull = document.getElementById('ull');
            obtn.onclick=function ()
            {
                if(oull.style.display=='none')
                {
                   oull.style.display='block'
                }
                else
                {
                    oull.style.display='none'
                }
            }
        }
    </script>
</head>
<body>
    <div id="box">
        <p id="btn" >标签1</p>
        <ul id="ull" style="display: block;">
            <li><a href="#">手写</a></li>
            <li><a href="#">拼音</a></li>
        </ul>
    </div>
</body>
</html>

效果如下