javascript 正则替换
var str = "<html><body><div>div内容</div><br>换行<br/><p>到底了</p></body></html>";
str = str.replace(/<(br[ ]?[/]?)>/g,"&_lt;$1&_gt;").replace(/</g,"&lt;").replace(/>/g,"&gt;").replace(/&_lt;/g,"<").replace(/&_gt;/g,">");
document.write(str);