用的浏览器内部转换器实现转换，方法是动态创建一个容器标签元素，如DIV，将要转换的字符串设置为这个元素的innerText(ie支持)||textContent(火狐支持)，然后返回这个元素的innerHTML，即得到经过HTML编码转换的字符串,显示的时候反过来就可以了（实际上显示的时候不用通过转换，直接赋值在div就可以正常显示的）。
<script type="text/javascript">
function HTMLEncode(html)
{
var temp = document.createElement ("div");
(temp.textContent != null) ? (temp.textContent = html) : (temp.innerText = html);
var output = temp.innerHTML;
temp = null;
return output;
}
function HTMLDecode(text)
{
var temp = document.createElement("div");
temp.innerHTML = text;
var output = temp.innerText || temp.textContent;
temp = null;
return output;
}
var html = "<br>dffdf<p>qqqqq</p>";
var encodeHTML = HTMLEncode(html);
alert("方式一：" + encodeHTML);
var decodeHTML = HTMLDecode(encodeHTML);
alert("方式一：" + decodeHTML);
</script>
<script type="text/javascript">
function HTMLEncode2(str)
{
var s = "";
if(str.length == 0) return "";
s = str.replace(/&/g,"&");
s = s.replace(/</g,"<");
s = s.replace(/>/g,">");
s = s.replace(/ /g," ");
s = s.replace(/\'/g,"'");
s = s.replace(/\"/g,""");
return s;
}
function HTMLDecode2(str)
{
var s = "";
if(str.length == 0) return "";
s = str.replace(/&/g,"&");
s = s.replace(/</g,"<");
s = s.replace(/>/g,">");
s = s.replace(/ /g," ");
s = s.replace(/'/g,"\'");
s = s.replace(/"/g,"\"");
return s;
}
var html = "<br>ccccc<p>aaaaa</p>";
var encodeHTML = HTMLEncode2(html);
alert("方式二：" + encodeHTML);
var decodeHTML = HTMLDecode2("方式二：" + encodeHTML);
alert(decodeHTML);
</script>
