Object.getOwnPropertyNames()

Il metodo Object.getOwnPropertyNames() ritorna un array di tutte le proprietà (incluse le proprietà non enumerabili, eccetto per quelle che utilizzano Simboli) trovate direttamente nell'oggetto.

Sintassi

Object.getOwnPropertyNames(obj)

Parametri

obj

L'oggetto le cui proprietà enumerabili e non enumrabili saranno ritornate come valori

Valori restituiti

Un array di stringhe che corrisponde alle proprietà trovate direttamente nell'oggetto passato

Description

Object.getOwnPropertyNames() returns an array whose elements are strings corresponding to the enumerable and non-enumerable properties found directly in a given object obj. The ordering of the enumerable properties in the array is consistent with the ordering exposed by a for...in loop (or by Object.keys()) over the properties of the object. The ordering of the non-enumerable properties in the array and th ordering among the enumerable properties is not defined.

Examples

Using Object.getOwnPropertyNames()

var arr = ['a', 'b', 'c'];
console.log(Object.getOwnPropertyNames(arr).sort()); 
// logs ["0", "1", "2", "length"]

// Array-like object
var obj = { 0: 'a', 1: 'b', 2: 'c' };
console.log(Object.getOwnPropertyNames(obj).sort()); 
// logs ["0", "1", "2"]

// Logging property names and values using Array.forEach
Object.getOwnPropertyNames(obj).forEach(
  function (val, idx, array) {
    console.log(val + ' -> ' + obj[val]);
  }
);
// logs
// 0 -> a
// 1 -> b
// 2 -> c

// non-enumerable property
var my_obj = Object.create({}, {
  getFoo: {
    value: function() { return this.foo; },
    enumerable: false
  }
});
my_obj.foo = 1;

console.log(Object.getOwnPropertyNames(my_obj).sort()); 
// logs ["foo", "getFoo"]

If you want only the enumerable properties, see Object.keys() or use a for...in loop (note that this will also return enumerable properties found along the prototype chain for the object unless the latter is filtered with hasOwnProperty()).

Items on the prototype chain are not listed:

function ParentClass() {}
ParentClass.prototype.inheritedMethod = function() {};

function ChildClass() {
  this.prop = 5;
  this.method = function() {};
}
ChildClass.prototype = new ParentClass;
ChildClass.prototype.prototypeMethod = function() {};

console.log(
  Object.getOwnPropertyNames(
    new ChildClass() // ["prop", "method"]
  )
);

Get non-enumerable properties only

This uses the Array.prototype.filter() function to remove the enumerable keys (obtained with Object.keys()) from a list of all keys (obtained with Object.getOwnPropertyNames()) thus giving only the non-enumerable keys as output.

var target = myObject;
var enum_and_nonenum = Object.getOwnPropertyNames(target);
var enum_only = Object.keys(target);
var nonenum_only = enum_and_nonenum.filter(function(key) {
  var indexInEnum = enum_only.indexOf(key);
  if (indexInEnum == -1) {
    // Not found in enum_only keys,
    // meaning that the key is non-enumerable,
    // so return true so we keep this in the filter
    return true;
  } else {
    return false;
  }
});

console.log(nonenum_only);

Notes

In ES5, if the argument to this method is not an object (a primitive), then it will cause a TypeError. In ES2015, a non-object argument will be coerced to an object.

Object.getOwnPropertyNames('foo');
// TypeError: "foo" is not an object (ES5 code)

Object.getOwnPropertyNames('foo');
// ["0", "1", "2", "length"]  (ES2015 code)

Specifications

Browser compatibility

Firefox-specific notes

Prior to Firefox 28, Object.getOwnPropertyNames did not see unresolved properties of Error objects. This has been fixed in later versions (bug 724768).

See also

• Enumerability and ownership of properties
• Object.prototype.hasOwnProperty()
• Object.prototype.propertyIsEnumerable()
• Object.create()
• Object.keys()
• Array.forEach()