Getting JavaScript object key list


I have a JavaScript object like

var obj = {
   key1: 'value1',
   key2: 'value2',
   key3: 'value3',
   key4: 'value4'
}

How can I get the length and list of keys in this object?

var obj = {
   key1: 'value1',
   key2: 'value2',
   key3: 'value3',
   key4: 'value4'
};
var keys = [];

for (var k in obj) keys.push(k);

alert("total " + keys.length + " keys: " + keys);


var obj = {
   key1: 'value1',
   key2: 'value2',
   key3: 'value3',
   key4: 'value4'
}
var keys = Object.keys(obj);
console.log('obj contains ' + keys.length + ' keys: '+  keys);

It's supported on most major browsers now.


Underscore.js makes the transformation pretty clean:

var keys = _.map(x, function(v, k) { return k; });

Edit: I missed that you can do this too:

var keys = _.keys(x);

If you only want the keys which are specific to that particular object and not any derived prototype properties:

function getKeys(obj) {
    var r = []
    for (var k in obj) {
        if (!obj.hasOwnProperty(k)) 
            continue
        r.push(k)
    }
    return r
}

e.g:

var keys = getKeys({'eggs': null, 'spam': true})
var length = keys.length // access the `length` property as usual for arrays

var keys = new Array();
for(var key in obj)
{
   keys[keys.length] = key;
}

var keyLength = keys.length;

to access any value from the object, you can use obj[key];


obj = {'a':'c','b':'d'}

You can try:

[index for (index in obj)] 

this will return:

['a','b']

to get the list of keys or

[obj[index] for (index in obj)]

to get the values


Anurags answer is basically correct. But to support Object.keys(obj) in older browsers as well you can use the code below that is copied from https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/keys . It adds the Object.keys(obj) method if it's not available from the browser.

if (!Object.keys) {
 Object.keys = (function() {
 'use strict';
 var hasOwnProperty = Object.prototype.hasOwnProperty,
    hasDontEnumBug = !({ toString: null }).propertyIsEnumerable('toString'),
    dontEnums = [
      'toString',
      'toLocaleString',
      'valueOf',
      'hasOwnProperty',
      'isPrototypeOf',
      'propertyIsEnumerable',
      'constructor'
    ],
    dontEnumsLength = dontEnums.length;

return function(obj) {
  if (typeof obj !== 'object' && (typeof obj !== 'function' || obj === null)) {
    throw new TypeError('Object.keys called on non-object');
  }

  var result = [], prop, i;

  for (prop in obj) {
    if (hasOwnProperty.call(obj, prop)) {
      result.push(prop);
    }
  }

  if (hasDontEnumBug) {
    for (i = 0; i < dontEnumsLength; i++) {
      if (hasOwnProperty.call(obj, dontEnums[i])) {
        result.push(dontEnums[i]);
      }
    }
  }
  return result;
};
}());
}

Note that in coffeescript this can be accomplished in all browsers and node as

k for k of obj

and thus

(1 for _ of obj).length

Use Object.keys()... it's the way to go.

Full documentation is available on the MDN site linked below:

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/keys


For a comma-delineated string listing the keys of a JSON Object, try the following:

function listKeys(jObj){
    var keyString = '';
    for(var k in jObj){
        keyString+=(','+k);
    }
    return keyString.slice(1);
}



/* listKeys({'a' : 'foo', 'b' : 'foo', 'c' : 'foo'}) -> 'a,b,c' */

Recursive solution for browsers that support ECMAScript 5:

var getObjectKeys = function(obj) {
    var keys = Object.keys(obj);
    var length = keys.length;

    if (length !== 0) {
        for (var i = 0; i < length; i++) {
            if (typeof obj[keys[i]] === 'object') {
                keys[keys[i]] = getObjectKeys(obj[keys[i]]);
            }
        }
    }

    return keys;
};

Using ES6, you can use forEach to iterate over the Keys of an Object. To get all the keys you can use Object.keys which returns all the keys in an Object

Object.keys(obj).forEach(function(keyValue, index, map) { 
  console.log(keyValue); 
});

Short hand of the above snippet would be, which only takes one parameter

Object.keys(obj).forEach(function(keyValue) { 
  console.log(keyValue); 
});

var obj = {
   key1: 'value1',
   key2: 'value2',
   key3: 'value3',
   key4: 'value4'
}

console.log(Object.keys(obj));
console.log(Object.keys(obj).length)

If you decide to use Underscore.js you better do

var obj = {
    key1: 'value1',
    key2: 'value2',
    key3: 'value3',
    key4: 'value4'
}

var keys = [];
_.each( obj, function( val, key ) {
    keys.push(key);
});
console.log(keys.lenth, keys);

In JavaScript, an object is a standalone entity, with properties and type.

For fetching values from Object in form of array: Object.values(obj) // obj is object name that you used Result -> ["value1", "value2", "value3", "value4"]

For fetching keys from Object in form of array: Object.keys(obj) // obj is object name that you used Result -> ["key1", "key2", "key3", "key4"]

As both functions are returning array you can get the length of keys or value by using length property. For instance - Object.values(obj).length or Object.keys(obj).length


using slice, apply and join method.

var print = Array.prototype.slice.apply( obj );
alert('length='+print.length+' list'+print.join());

       if(props.userType){
          var data = []
          Object.keys(props.userType).map(i=>{
                data.push(props.userType[i])
          })
          setService(data)
        }