更改对象JavaScript中数组的位置

Question

I have an object 'test' :

var test={
   "unit3":[
      {
         "chapter":{
            "id":4,
            "name":"earth",
            "id_above":2
         }
      },
      {
         "book":{"name":"earth"}
      }
   ],
   "unit4":[
      {
         "chapter":{
            "id":5,
            "name":"water",
            "id_above":2
         }
      },
      {
         "book":{"name":"sea"}
      }
   ],
   "unit1":[
      {
         "chapter":{
            "id":2,
            "name":"biology",
            "id_above":2
         }
      },
      {
         "book":{"name":"science"}
      }
   ]
};

According to 'id_above value' (id_above and id should be same , if not, I have to move it under the right unit), I would like to get this :

 var hope={
  "unit1":[
    {
      "chapter":{
        "id":2,
        "name":"biology",
        "id_above":2
      }
    },
    {
      "book":{"name":"science"}
    }
  ],
  "sub":[
    {
      "unit3":[
        {
          "chapter":{
            "id":4,
            "name":"earth",
            "id_above":2
          }
        },
        {
          "book":{"name":"earth"}
        }
      ],
      "unit4":[
        {
          "chapter":{
            "id":5,
            "name":"water",
            "id_above":2
          }
        },
        {
          "book":{"name":"sea"}
        }
      ]
    }
  ]
}

I tried :

   for (var key in test){
   if(test.hasOwnProperty(key)){
   for (var i =0;i<test[key].length;i++){
   if (test[key][i].chapter.id!=test[key][i].chapter.id_above){


   for (var key2 in test){
    if(test.hasOwnProperty(key2)){
    for (var j =0;j<test[key2].length;j++){
    var o=_.find(test[key2][j].chapter,{id:test[key][i].chapter.id_above})
    console.log("o",o); //undefined
    } }}}   } } }

The problem is that my variable o is 'undefined' , I would like to do after something like:

test.sub=a;         

Could you help me please ? Thanks.

Answer 1

You can't readily use JavaScript objects as ordered containers. Instead, use an array.

While it's true that JavaScript object properties have an order now (or that some operations act as though object properties have an order now, depending on how you want to look at it), that's a new thing (as of ES2015) and that order is difficult to work with. Notably, the for-in statement does not support property order, nor does Object.keys . Some new operations such as Object.getOwnPropertyNames do support the new order.

When you want an order, use an array.