checkbox的全選和取消全選按鈕的js

<span style="font-size:18px;">//全選、取消全選
	function selectAll() {
		var checked = $("#checkall").attr("checked");
		$("input[name='checkbox_name']").each(function() {
			if (checked) {
				$(this).attr("checked", "checked");//全選
				if (allarr.length > 0) {
					for ( var i = 0; i < allarr.length; i++) {
						if (allarr[i] != $(this).val()) {
							allarr.push($(this).val());
							break;
						}
					}
				} else {
					allarr.push($(this).val());
				}
			} else {
				$(this).removeAttr("checked");//取消全選
				for ( var i = 0; i < allarr.length; i++) {
					if (allarr[i] == $(this).val()) {
						allarr.splice(i, 1);
					}
				}
			}
		</span>});
	}