Access multilevel key from a JSON object in javascript

Question

I have a javascript function which returns the response like this( I am using nodejs and ejs):

"index_1": {
    "mappings": {
        "type_1": {
            "properties": {
                "field_1": {
                    "type": "string"
                },
                "field_2": {
                    "type": "string"
                }
            }
        },
        "type_2": {
            "properties": {
                "field_1": {
                    "type": "string"
                },
                "field_2": {
                    "type": "string"
                },
                "field_3": {
                    "type": "string"
                }
            }
        }
    }
}

Now, I need to access 2nd or third level key from the response. Suppose if I want a list like this:

type_1
type_2

or

field_1
field_2
field_3

How can I do that? If I use callback(Object.keys(response)) then it returns index_1. Can anyone point me to right direction?

Do you need a particular field or type, or would you like to perform something for each of them? — Hodrobond
– Hodrobond, Commented Jan 20, 2017 at 15:43

TimoStaudinger · Accepted Answer · 2017-01-20 15:47:40Z

1

To get the keys of a sub-object, you need to pass this particular sub-object to Object.keys():

var data = {"index_1":{"mappings":{"type_1":{"properties":{"field_1":{"type":"string"},"field_2":{"type":"string"}}},"type_2":{"properties":{"field_1":{"type":"string"},"field_2":{"type":"string"},"field_3":{"type":"string"}}}}}};

console.log(Object.keys(data.index_1.mappings));                   
    // ["type_1", "type_2"]

console.log(Object.keys(data.index_1.mappings.type_2.properties)); 
    // ["field_1", "field_2", "field_3"]

answered Jan 20, 2017 at 15:47

TimoStaudinger

42.7k16 gold badges91 silver badges96 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Sebastian Brud · Accepted Answer · 2017-01-20 16:07:11Z

There is no simple one-liner, I suppose.

Object.keys( object );

returns only first level keys (that's the reason you get index_1).

Solution 1

If you know, that response, has alway a structure of:

var jsonObject = {
   "index_1" : { 
       "mappings": {
            "type1" : ... ,
            "type2" : ...
       }
};

Then you only need to pass:

callback(Object.keys(jsonObject.index1.mappings));

That way you'll get third level keys.

But if you don't know the structure, or want to access keys of any level, then recursion might be helpful.

var jsonObject = {
   "index_1" : {
       "mappings": {
            "type1" : { field1 : {}, field2 : 2} ,
            "type2" : {}
       }
   }
};

// 1..N, and 1 means you want to get **index_1**
function getNthLevelKeys( json, level ) {
      var keys = [];
      var currLvlKeys = Object.keys(json);
      level = level - 1;

      if ( typeof json !== 'object' || json === null) {
          return [];
      }

      if ( level > 0 ) {

           for (var i = 0; i < currLvlKeys.length; i++) {
               keys = keys.concat(getNthLevelKeys( json[ currLvlKeys[i] ] , level ));
            }
      }

      if (level === 0) {
            return currLvlKeys;
      }

      if (level < 0) {
           throw new Error("Cannot access level "+level+" of this object");
      }

      return keys;
}

console.log(getNthLevelKeys( jsonObject , 1));
console.log(getNthLevelKeys( jsonObject , 2));
console.log(getNthLevelKeys( jsonObject , 3));
console.log(getNthLevelKeys( jsonObject , 4));

Collectives™ on Stack Overflow

Access multilevel key from a JSON object in javascript

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related