First class ,6 examples anlaysisi

2022-10-08 19:23:59

http://www.fgm.cc/learn/

First class ,6 examples anlaysisi

 <!DOCTYPE html>

 <!--

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 <html>

     <head>

         <title>Change Attribute?</title>

         <meta charset="UTF-8">

         <meta name="viewport" content="width=device-width, initial-scale=1.0">

         <style>

             * {

                 padding:0;

                 margin:0;

             }

             #changeAttr{

                 width:370px;

                 /*width:auto or 100%, not center*/

                 margin:100px auto;

                 border:1px solid #000000;

                 padding:50px;

             }

             #obj{

                 width:150px;

                 margin:20px auto;

                 height:150px;

                 background-color:black;

             }

         </style>

     </head>

     <body>

         <div id='changeAttr'>

             <h1>Change Attribute</h1>

             <div id='content'>

                 <input id='chWidth' type='button' value='CH WIDTH'/>

                 <input id='chHeight' type='button' value='CH HIGHT'/>

                 <input id='chColor' type='button' value='CH COLOR'/>

                 <input id='chHide' type='button' value='CH HIDE'/>

                 <input id='chReset' type='button' value='CH RESET'/>

                 <div id='obj'></div>

             </div>

         </div>

         <script>

 //            window.onload = function(){

 //                var chWidth = document.getElementById("chWidth");

 //                var chHeight = document.getElementById("chHeight");

 //                var chColor = document.getElementById("chColor");

 //                var chHide = document.getElementById("chHide");

 //                var chReset = document.getElementById("chReset");

 //                var obj = document.getElementById("obj");

 //

 //                chWidth.onclick = function(){

 //                    obj.style.width = '300px';

 //                }

 //                chHeight.onclick = function(){

 //                    obj.style.height = '300px';

 //                }

 //                chColor.onclick = function(){

 //                    obj.style.backgroundColor = '#ff0000';

 //                }

 //                chHide.onclick = function(){

 //                    obj.style.display = 'none';

 //                }

 //                chReset.onclick = function(){

 //                    obj.style.width = '150px';

 //                    obj.style.height = '150px';

 //                    obj.style.backgroundColor = '#000000';

 //                    obj.style.display = 'block';

 //                }

 //            }

 //            var changeStyle = function (elem, attr, value)

 //            {

 //                    elem.style[attr] = value

 //            };

 //            window.onload = function ()

 //            {

 //                    var oBtn = document.getElementsByTagName("input");

 //                    var oDiv = document.getElementById("obj");

 //                    var oAtt = ["width","height","background","display","display"];

 //                    var oVal = ["200px","200px","red","none","block"];

 //

 //                    for (var i = 0; i < oBtn.length; i++)

 //                    {

 //                            oBtn[i].index = i;

 //                            oBtn[i].onclick = function ()

 //                            {

 //                                    this.index == oBtn.length - 1 && (oDiv.style.cssText = "");

 //                                    console.log(this.index);

 //                                    changeStyle(oDiv, oAtt[this.index], oVal[this.index])

 //                            }

 //                    }

 //            };

             var changeStyle = function(ele,attr,val){

                 ele.style[attr] = val;

             };

             window.onload = function(){

                 var oBtn = document.getElementsByTagName("input");

                 var oDiv = document.getElementById("obj");

                 var oAttr = ["width","height","backgroundColor","display","display"];

                 var oVal = ["200px","200px","red","none","block"];

                 for(var i=0;i<oBtn.length;i++){

                     oBtn[i].index = i;

                     oBtn[i].onclick = function(){

                         this.index == oBtn.length - 1 && (oDiv.style.cssText = "");

                         //console.log(this.index);

                         changeStyle(oDiv,oAttr[this.index],oVal[this.index]);

                     };

                 }

             }

         </script>

     </body>

 </html>

1.width auto or 100%, not center;

2.good at using for ,like getElementsByTagName('input');

3.this.index == oBtn.length - 1 && (oDiv.style.cssText = ""); like

　　if(a >=5){
　　alert("你好");
　　}
　　可以写成：
　　a >= 5 && alert("你好");

4. look at 3,oDiv.style.cssText = "",all recover,it means add style through js,then the style go to html lines, when you clean style,you just clean style inline,not the style in<style> or stylesheet.

1.首次打开页面时候便已有默认风格
　　不好：在全局里面设置一次风格，然后在onclick里面在写一遍同样的代码
　　改进：在<style>先给风格，只是以后点击会更换风格，减少代码量

2.border:横排有重复边
　　不好：给每个子元素每边都加，然后统一去掉右边框，最好给父元素或最后一个子加一个右边框
　　改进：父每边都有，子统一有右边框，最后去掉最后子的右边框；来回折腾的减少
3.<li>red</li> 加text-indent：-9999px；方便理解

4.去掉外层div ，当里面li：float：left时，ul仍然可以包住li
5.<a href="javascript:;"></a>

1. input 前必须加#content，否则margin-bottom会被#content中的margin覆盖，（优先级不够），by the way,有padding好看多了

#################################################################################

1.text-align：center，对div：block不管用，对inline-block管用
2.子元素float之后，父{width:xxxpx;margin:0 auto;},此时虽然没有包住子，但子依然居中；父加上height，就包住子

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