如何使用 Object.keys()？

Question

我通常习惯于使用 Object.keys() 函数。 但是这一次，对于以下 JSON 中的每个对象，我无法按名称读取属性的值：

JSON

var myData = {
  "customNotes":{
    "2017/04/17":{
      "concernedDate":"April, 17, 2017",
      "notesList":[
        {
          "id":25,
          "title":"Note 25 Title"
        },
        {
          "id":51,
          "title":"Note 51 Title"
        }
      ]
    },
    "2017/04/14":{
      "concernedDate":"April, 14, 2017",
      "notesList":[
        {
          "id":53,
          "title":"Note 53 Title"
        }
      ]
    }
  }
}

我需要的输出

我需要的是以下输出：

    2017/04/17
    concernedDate: April, 17, 2017
    Number of notes: 2
    Notes list:
    - id: 25
    - title: Note 25 Title
    - id: 51
    - title: Note 51 Title
    - - - - - - - -
    2017/04/14
    concernedDate: April, 14, 2017
    Number of notes: 1
    Notes list:
    - id: 53
    - title: Note 53 Title

我的错误 JS 代码

$(Object.keys(myData.customNotes)).each(function(iGroup){

    //Get Key/Val of each Group of notes
    var keyGroup = Object.keys(myData.customNotes)[iGroup];
    var valGroup = myData.customNotes[keyGroup];

    //Print Key (the date as a string)
    console.log(valGroup[0]);

    //Print Key Property ('concernedDate')
    console.log('concernedDate: ' + valGroup[0].concernedDate);

    //Print Key Property Length ('notesList')
    console.log('Number of notes: ' + valGroup[0].notesList.length);

    //Print List of notes
    console.log('Notes list:');

    //If the property exists
    if(valGroup[0].notesList){
        //For each item in 'notesList'
        $(Object.keys(valGroup[0].notesList)).each(function(iNote){

            //Get Key/Val For each note
            var keyNote = Object.keys(valGroup[0].notesList)[iNote];
            var valNote = valGroup[0].notesList[keyNote];

            //Print the properties of each note
            console.log('- id: ' + valNote.id);
            console.log('- title: ' + valNote.title);
        });
    }

});

Answer 1

排序

在我的对象中添加了一些元素后，我需要按 KEY 对其进行排序（日期：例如 2017/04/17）。

但无论我尝试什么，它总是以相同的顺序返回相同的项目：

//Creating an Array of SORTED values (Nothing works :-/)
var tmpArr = Object.keys(myData.customNotes).sort((a, b) => a > b ? a : b);
var tmpArr = Object.keys(myData.customNotes).sort((a, b) => Date(a).valueOf() > Date(b).valueOf() ? a : b);
var tmpArr = Object.keys(myData.customNotes).sort((a, b) => a.valueOf() > b.valueOf() ? a : b);
var tmpArr = Object.keys(myData.customNotes).sort((a, b) => a-b);


//Convert back the Array to an Object
var myData.customNotes = tmpArr.reduce(function(acc, cur, i) {
  acc[i] = cur;
  return acc;
}, {});

Answer 2

首先，我要感谢@cheestherapy 的回答：它就像一个魅力，你绝对应该依赖它，无论它是在 ES6 还是 ES5 中！

同时，我自己进行了实验，发现另一种可行的解决方案，以更“经典的循环风格”方式实现结果相同。

另一种工作方法（更经典）

因此，对于那些希望在脚本的每一步拥有更多控制权的人来说，这里是另一种可行的方法：

//WORKING
console.log('---START LIST---');

//For each GROUP OF NOTES
for (var item in myData.customNotes) {
    //Print GROUP OF NOTES key
    console.log(item);

    //Print GROUP OF NOTES properties
    console.log('concernedDate: ' + myData.customNotes[item].concernedDate);
    console.log('Number of notes: ' + myData.customNotes[item].notesList.length);
    console.log('Notes list: ');

    //For each NOTE
    $(Object.keys(myData.customNotes[item].notesList)).each(function(iGroup){

        //Get this Array item
        var keyGroup = Object.keys(myData.customNotes[item].notesList)[iGroup];
        var valGroup = myData.customNotes[item].notesList[keyGroup];

        //Print NOTE properties
        console.log('- id: ' + valGroup.id);
        console.log('- title: ' + valGroup.title);

    });
    console.log('- - - - - -');

}
console.log('---END LIST---');

Answer 3

es6

Object.keys(myData.customNotes).reduce((prev, curr) => {
    const date = curr;
    const concernedDate = myData.customNotes[curr].concernedDate;
    const numberNotes = myData.customNotes[curr].notesList.length;
    const notesList = myData.customNotes[curr].notesList.map(note => `- id: ${note.id} \n - title: ${note.title} \n\n`);

    return prev + `${date} \n ${concernedDate} \n Number of notes: ${numberNotes} \n Notes list: \n ${notesList} \n - - - - - - - - \n`;
   }, ''));

es5

Object.keys(myData.customNotes).reduce(function (prev, curr) {
    const date = curr;
    const concernedDate = myData.customNotes[curr].concernedDate;
    const numberNotes = myData.customNotes[curr].notesList.length;
    const notesList =        myData.customNotes[curr].notesList.map(function(note) { return  ‘- id: ‘ +  note.id + ‘\n’ + ‘- title: ‘ + note.title + ‘\n\n’;});

    return prev + 'date' +  '\n' + concernedDate +  '\n Number of notes: ' + numberNotes +  '\n Notes list: \n' + notesList + ' \n - - - - - - - - \n';
}, ''));