How to traverse JSON object locating particular property and pushing its contents to array?

Question

I am working with a JSON object which can have a property ids at any leaf. I want to traverse the object and find all of the instances of the ids property and store each id in a collection.

Mocked up JSON Object (the ids property could be at much deeper property locations).

{
  "id": "b38a683d-3fb6-408f-9ef6-f4b853ed1193",
  "foo": {
    "ids": [
      {
        "id": "bd0bf3bd-d6b9-4706-bfcb-9c867e47b881"
      },
      {
        "id": "d1cc529d-d5d2-4460-b2bb-acf24a7c5999"
      },
      {
        "id": "b68d0c8c-548e-472f-9b01-f25d4b199a71"
      }
    ],
    "baz": "super"
  },
  "bar": {
    "ids": [
      {
        "id": "bd0bf3bd-d6b9-4706-bfcb-9c867e47b881"
      },
      {
        "id": "d1cc529d-d5d2-4460-b2bb-acf24a7c5999"
      },
      {
        "id": "b68d0c8c-548e-472f-9b01-f25d4b199a71"
      }
    ]
  }
}

I am using the following code to traverse the above JSON.

var jsonFile = require('./file_test.json'); // the above in my local directory

function traverse(obj, ids) {
  for (var prop in obj) {
    if (typeof obj[prop] == "object" && obj[prop]) {
      if (prop == 'ids') {
        for (var i = obj[prop].length - 1; i >= 0; i--) {
          ids.push(obj[prop][i]._id);
        };
      }
      traverse(obj[prop], ids);
    }
  }
}

var ids = new Array();
traverse(jsonFile, ids);

console.log('ids', ids);

The above nets the following:

ids
[
  'b68d0c8c-548e-472f-9b01-f25d4b199a71',
  'd1cc529d-d5d2-4460-b2bb-acf24a7c5999',
  'bd0bf3bd-d6b9-4706-bfcb-9c867e47b881',
  'b68d0c8c-548e-472f-9b01-f25d4b199a71',
  'd1cc529d-d5d2-4460-b2bb-acf24a7c5999',
  'bd0bf3bd-d6b9-4706-bfcb-9c867e47b881'
]

While my code works I am not convinced that I am doing this the most efficient or best way. Is there a better way to find all instances of the ids property? Perhaps without passing in an array but returning one? Or setting up for a callback with an ids array?

Solution 1

If the data was actually a JSON string, and not a JavaScript object, you could have something like:

// assuming `json` is the data string
var ids = [];
var data = JSON.parse(json, function(key, value) {
    if (key === "id") 
        ids.push(value);

    return value;
});

See reviver on JSON.parse method.

Solution 2

what you have is fine, but this is a little shorter and uses the .map function:

var jsonFile = require('./file_test.json'); // the above in my local directory
function traverse(obj) {
    var ids = [];
    for (var prop in obj) {
        if (typeof obj[prop] == "object" && obj[prop]) {
            if (prop == 'ids') {
                ids = obj[prop].map(function(elem){
                   return elem.id;
               })
            }
            ids =ids.concat(traverse(obj[prop]));
        }
    }
    return ids;
}

var ids =traverse(jsonFile);

console.log('ids', ids);