<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
</head>
<body>
<script type="text/javascript">
function trim() {
var start = 0;
var end = this.length - 1;
while(start<=end && this.charAt(start)==" ") {
start++;
}
while(start<=end && this.charAt(end)==" ") {
end--;
}
return this.subString(start,end+1);
}
String.prototype.trim = trim;
var a = " abc ";
alert(a.trim());
</script>
</body>
</html>