letmath={subject:'数学',children:[{id:1,title:'一号'},{id:2,title:'二号'},{id:3,title:'数三'},{id:0,title:'待定'}]}//获取对象的属性数Object.getOwnPropertyNames(math).length;Object.键(数学).length;

letmath={subject:'数学',children:[{id:1,title:'一号'},{id:2,title:'二号'},{id:3,title:'数三'},{id:0,title:'待定'}]}//获取对象的属性数Object.getOwnPropertyNames(math).length;Object.键(数学).length;