Enumerability and ownership of properties

Enumerable properties are those which can be iterated by a for..in loop. Ownership of properties is determined by whether the property belongs to the object directly and not to its prototype chain. Properties of an object can also be retrieved in total. There are a number of built-in means of detecting, iterating/enumerating, and retrieving object properties, with the chart showing which are available. Some sample code follows which demonstrates how to obtain the missing categories.

Functionality Own object Own object and its prototype chain Prototype chain only

Detection

Enumerable	Nonenumerable	Enumerable and Nonenumerable
`propertyIsEnumerable`	`hasOwnProperty` and not `propertyIsEnumerable`	`hasOwnProperty`

Not available without extra code

Retrieval

Enumerable	Nonenumerable	Enumerable and Nonenumerable
`Object.keys`	`getOwnPropertyNames` filtered to include properties when not passing `propertyIsEnumerable`	`getOwnPropertyNames`

Not available without extra code

Iteration

Enumerable	Nonenumerable	Enumerable and Nonenumerable
Iterate over `Object.keys`	Iterate over `getOwnPropertyNames` filtered to include properties when not passing `propertyIsEnumerable`	Iterate over `getOwnPropertyNames`

Enumerable	Nonenumerable	Enumerable and Nonenumerable
`for..in`	Not available without extra code	Not available without extra code

Not available without extra code

Obtaining properties by enumerability/ownership

Note that this is not the most efficient algorithm for all cases, but useful for a quick demonstration.

Detection can occur by SimplePropertyRetriever.theGetMethodYouWant(obj).indexOf(prop) > -1
Iteration can occur by SimplePropertyRetriever.theGetMethodYouWant(obj).forEach(function (value, prop) {}); (or use filter(), map(), etc.)

var SimplePropertyRetriever = {
    getOwnEnumerables: function (obj) {
        return this._getPropertyNames(obj, true, false, this._enumerable); 
         // Or could use for..in filtered with hasOwnProperty or just this: return Object.keys(obj);
    },
    getOwnNonenumerables: function (obj) {
        return this._getPropertyNames(obj, true, false, this._notEnumerable);
    },
    getOwnEnumerablesAndNonenumerables: function (obj) {
        return this._getPropertyNames(obj, true, false, this._enumerableAndNotEnumerable); 
        // Or just use: return Object.getOwnPropertyNames(obj);
    },
    getPrototypeEnumerables: function (obj) {
        return this._getPropertyNames(obj, false, true, this._enumerable);
    },
    getPrototypeNonenumerables: function (obj) {
        return this._getPropertyNames(obj, false, true, this._notEnumerable);
    },
    getPrototypeEnumerablesAndNonenumerables: function (obj) {
        return this._getPropertyNames(obj, false, true, this._enumerableAndNotEnumerable);
    },
    getOwnAndPrototypeEnumerables: function (obj) {
        return this._getPropertyNames(obj, true, true, this._enumerable); 
        // Or could use unfiltered for..in
    },
    getOwnAndPrototypeNonenumerables: function (obj) {
        return this._getPropertyNames(obj, true, true, this._notEnumerable);
    },
    getOwnAndPrototypeEnumerablesAndNonenumerables: function (obj) {
        return this._getPropertyNames(obj, true, true, this._enumerableAndNotEnumerable);
    },
    // Private static property checker callbacks
    _enumerable : function (obj, prop) {
        return obj.propertyIsEnumerable(prop);
    },
    _notEnumerable : function (obj, prop) {
        return !obj.propertyIsEnumerable(prop);
    },
    _enumerableAndNotEnumerable : function (obj, prop) {
        return true;
    },
    // Inspired by http://stackoverflow.com/a/8024294/271577
    _getPropertyNames : function getAllPropertyNames(obj, iterateSelfBool, iteratePrototypeBool, includePropCb) {
        var props = [];

        do {
            if (iterateSelfBool) {
                Object.getOwnPropertyNames(obj).forEach(function (prop) {
                    if (props.indexOf(prop) === -1 && includePropCb(obj, prop)) {
                        props.push(prop);
                    }
                });
            }
            if (!iteratePrototypeBool) {
                break;
            }
            iterateSelfBool = true;
        } while (obj = Object.getPrototypeOf(obj));

        return props;
    }
};

Detection Table

	`in`	`for..in`	`hasOwnProperty`	`propertyIsEnumerable`	`in Object.keys`	`in Object.getOwnPropertyNames`
Enumerable	true	true	true	true	true	true
Nonenumerable	true	false	true	false	false	true
Inherited Enumerable	true	true	false	false	false	false
Inherited Nonenumerable	true	false	false	false	false	false

Enumerability and ownership of properties

Obtaining properties by enumerability/ownership

Detection Table

See also

Document Tags and Contributors