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()
原文：http://www.cnblogs.com/kaituorensheng/p/4576729.html