获取所有checkbox的值，并去掉最后一个,

[javascript]代码库

var str = document.getElementsByName("box");
			for (i = 0; i < str.length; i++) {
				if (str[i].checked == true) {
					sb = sb + str[i].value;
					if (i < str.length) {
						sb = sb + ",";
					}
				}
			}
			var endpos = sb.lastIndexOf(',');
			if (endpos > -1) {
				sb = sb.substring(0, endpos)
						+ sb.substring(endpos + 1, sb.length);
			}