Object.getOwnPropertyNames()

Summary

The Object.getOwnPropertyNames() method returns an array of all properties (enumerable or not) found directly upon a given object.

Syntax

Object.getOwnPropertyNames(obj)

Parameters

obj

The object whose enumerable and non-enumerable own properties are to be returned.

Description

Object.getOwnPropertyNames returns an array whose elements are strings corresponding to the enumerable and non-enumerable properties found directly upon 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 among the enumerable properties, is not defined.

Examples

var arr = ["a", "b", "c"];
print(Object.getOwnPropertyNames(arr).sort()); // prints "0,1,2,length"

// Array-like object
var obj = { 0: "a", 1: "b", 2: "c"};
print(Object.getOwnPropertyNames(obj).sort()); // prints "0,1,2"

// Printing property names and values using Array.forEach
Object.getOwnPropertyNames(obj).forEach(function(val, idx, array) {
  print(val + " -> " + obj[val]);
});
// prints
// 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;

print(Object.getOwnPropertyNames(my_obj).sort()); // prints "foo, getFoo"

If you want only the enumerable properties, see Object.keys or use a for...in loop (although note that this will return enumerable properties not found directly upon that object but also 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 () {
};

alert(
  Object.getOwnPropertyNames(
    new ChildClass() // ["prop", "method"]
  )
)

Get Non-Enumerable 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) leaving only the non-enumerable keys.

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 mean the key is enumerable, so return true so we keep this in the filter
    return true;
  } else {
    return false;
  }
});
            
console.log(nonenum_only);

Specifications

Browser compatibility

Based on Kangax's compat table.

SpiderMonkey-specific notes

• Prior to SpiderMonkey 28 (Firefox 28 / Thunderbird 28 / SeaMonkey 2.25), 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()