checkbox
val = "<li class='layer'><label><input type='checkbox' checked name='layers' class='layerSelect' id='" + layers_name_list[i] + "'><span>" + layers_name_list[i] + "</span></label></li>"
items = document.getElementsByName("layers");
判断是否选中:items[0].checked;
设置选中:items[0].checked = true;
整形变字符串:String()
字符串变整形:Number()