对String对象进行扩展，使其具有去掉字符串前后空格的方法
通过正则表达式可以实现题目要求具体代码如下：
<html><head><script language="javascript">String.prototype.trim = function(){return this.replace(/^\s+|\s+$/g,"")}var testStr = " this is a dog ";alert("&&&&"+testStr.trim()+"&&&&");</script></head><body><div id="id1"><a href="#" onclick="aone('id1')">innerText</a></div><div id="id2"><a href="#" onclick="aone('id2')">innerHTML</a></div><div id="test"> <span style="color:red">test1</span> test2 </div> <a href="javascript:alert(test.innerHTML)">innerHTML</a> <a href="javascript:alert(test.innerText)">innerText</a> <a href="javascript:alert(test.outerHTML)">outerHTML</a></body></html>?