How can i get key of nested object = used For....in?

Question

Here is my code. How can i get the key of the key-value pair using for loop?

var apartment = {
  bedroom: {
    area: 20,
    bed: {
      type: 'twin-bed',
      price: 100
    }
  }
};

The desired output is as follows:

/* desired results :
 * bedroom
 * area
 * bed
 * type
 * price
*/

Please help

Check https://stackoverflow.com/questions/38083288/how-to-get-the-key-value-from-nested-object — Mohammad, Oct 29 '18 at 10:12
Possible duplicate of [Javascript get Object property Name](https://stackoverflow.com/questions/22565077/javascript-get-object-property-name) — Anthony Granger, Oct 29 '18 at 10:23

score 1 · Answer 1 · answered Oct 29 '18 at 10:20

1

var getKeys = function(obj) {
  var keys = [];
  Object.keys(obj).forEach(function(key){
    keys.push(key);
    if(typeof obj[key] == 'object'){
      keys = keys.concat(getKeys(obj[key]));
    }
  })
  return keys;
}

Then

var keys = getKeys(apartment);

answered Oct 29 '18 at 10:20

Cong Nguyen

3,199
1
23
22

Not sure what is "For ..in" means, but the return keys is an array and you can loop it. – Cong Nguyen Oct 29 '18 at 10:46

score 1 · Answer 2 · answered Oct 29 '18 at 10:24

You can use a simple Regex as follow:

var apartment = {
  bedroom: {
    area: 20,
    bed: {
      type: 'twin-bed',
      price: 100
    }
  }
};
 let result = [];
 let jsonstr = JSON.stringify(apartment);
 // {"bedroom":{"area":20,"bed":{"type":"twin-bed","price":100}}}
 let regex = /"(\w+)":/g;
 jsonstr.replace(regex, function(match,prop){
   result.push(prop);
 });
 console.log(result);

score 1 · Answer 3 · answered Oct 29 '18 at 12:04

we can easily done by using regex, convert object string and apply regex to extract the particular word

run the snippet for required output

var apartment = {
  bedroom: {
    area: 20,
    bed: {
      type: 'twin-bed',
      price: 100
    }
  }
};

apartment = JSON.stringify(apartment);

var re = /(")\w+(")(:)/g;
var match;
do {
    match = re.exec(apartment);
    if (match) {
        console.log(match[0]);
    }
} while (match);

regex : /(")\w+(")(:)/g

only extracts key for more click here

do while loop responsible to detect multiple match in the string

score 0 · Answer 4 · answered Oct 29 '18 at 10:18

var inputs = [
  {a:1,b:2,c:3}, // Simple object
  {a:{b:2,c:3}}, // Simple object with nesting
  {a:{a:{b:2,c:3}}}, // Repeated key hiding nesting
  {a:[{b:2,c:3}]}, // keys behind array
];
inputs.push(inputs); // reference cycle and array at top

function getKeys(obj) {
  var all = {};
  var seen = [];
  checkValue(obj);
  return Object.keys(all);

  function checkValue(value) {
    if (Array.isArray(value)) return checkArray(value);
    if (value instanceof Object) return checkObject(value);
  }

  function checkArray(array) {
    if (seen.indexOf(array) >= 0) return;
    seen.push(array);
    for (var i = 0, l = array.length; i < l; i++) {
      checkValue(array[i]);
    }
 }

  function checkObject(obj) {
    if (seen.indexOf(obj) >= 0) return;
    seen.push(obj);
    var keys = Object.keys(obj);
    for (var i = 0, l = keys.length; i < l; i++) {
      var key = keys[i];
      all[key] = true;
      checkValue(obj[key]);
    }
  }
}

var result = inputs.map(getKeys);

console.log(result);

score 0 · Accepted Answer · answered Oct 29 '18 at 10:32

You can use a recursive function :

function getKeys(source, dest) {
    for (let key in source) {
        if (typeof source[key] == 'object') {
            dest.push(key)
            getKeys(source[key], dest)
        } else { 
            dest.push(key)
        }
    } 
    return dest 
}

result = []
const apartment = {
  bedroom: {
    area: 20,
    bed: {
      type: 'twin-bed',
      price: 100
    }
  }
}
getKeys(apartment, result) // ["bedroom", "area", "bed", "type", "price"]

How can i get key of nested object = used For....in?

5 Answers5