javascript字符串函数

<script type="text/javascript">

var str="Hello world!"
document.write(str.substring(3,7))

</script>

var str="Hello world!"
document.write(str.substring(3))

var str="Visit Microsoft!"
document.write(str.replace(/Microsoft/, "W3School"))

返回
Visit W3School!

<script language="javascript">

  var strSrc = "a12b34c56";

  var re = /(\d)(\d)/gi;

  var strDest = strSrc.replace(re,"$2$1");

  alert(strSrc + " has been converted into " + strDest);

</script>

String.prototype.trim = function(){
return this.replace(/^\s+|\s+$/g,"");

}; 
alert("  aaa  ".trim());