//用来截取等长字符串。在网页中显示的时候,所占的长度相等
//中文占2位,英文占一位.以英文为标准.
function getSubstr (old , len) {
	if (old == null)// || len >= old.length)
		return old;
	var subTo = 0;
	var index = 0;
	
	for (var i = 0 ; i < old.length ; i++){
		var chr = old.charAt(i);
		var chrCd = old.charCodeAt(i);
		if (chrCd >=0 && chrCd <= 128)
			index ++;
		else
			index += 2;
		if(index > len)
			break;
		subTo ++;
	}//end for
	return old.substr(0,subTo);
}