Querying object properties

There are four built-in ways to query a property of an object. They all support both string and symbol keys. The following table summarizes when each method returns true.

	Enumerable, own	Enumerable, inherited	Non-enumerable, own	Non-enumerable, inherited
`propertyIsEnumerable()`	`true ✅`	`false ❌`	`false ❌`	`false ❌`
`hasOwnProperty()`	`true ✅`	`false ❌`	`true ✅`	`false ❌`
`Object.hasOwn()`	`true ✅`	`false ❌`	`true ✅`	`false ❌`
`in`	`true ✅`	`true ✅`	`true ✅`	`true ✅`

There are many methods in JavaScript that traverse a group of properties of an object. Sometimes, these properties are returned as an array; sometimes, they are iterated one-by-one in a loop; sometimes, they are used for constructing or mutating another object. The following table summarizes when a property may be visited.

Methods that only visit string properties or only symbol properties will have an extra note. ✅ means a property of this type will be visited; ❌ means it will not.

	Enumerable, own	Enumerable, inherited	Non-enumerable, own	Non-enumerable, inherited
`Object.keys` `Object.values` `Object.entries`	✅ (strings)	❌	❌	❌
`Object.getOwnPropertyNames`	✅ (strings)	❌	✅ (strings)	❌
`Object.getOwnPropertySymbols`	✅ (symbols)	❌	✅ (symbols)	❌
`Object.getOwnPropertyDescriptors`	✅	❌	✅	❌
`Reflect.ownKeys`	✅	❌	✅	❌
`for...in`	✅ (strings)	✅ (strings)	❌	❌
`Object.assign` (After the first parameter)	✅	❌	❌	❌
Object spread	✅	❌	❌	❌

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).includes(prop)
Iteration can occur by SimplePropertyRetriever.theGetMethodYouWant(obj).forEach((value, prop) => {}); (or use filter(), map(), etc.)

const SimplePropertyRetriever = {
  getOwnEnumProps(obj) {
    return this._getPropertyNames(obj, true, false, this._enumerable);
    // Or could use for...in filtered with Object.hasOwn or just this: return Object.keys(obj);
  },
  getOwnNonEnumProps(obj) {
    return this._getPropertyNames(obj, true, false, this._notEnumerable);
  },
  getOwnProps(obj) {
    return this._getPropertyNames(
      obj,
      true,
      false,
      this._enumerableAndNotEnumerable,
    );
    // Or just use: return Object.getOwnPropertyNames(obj);
  },
  getPrototypeEnumProps(obj) {
    return this._getPropertyNames(obj, false, true, this._enumerable);
  },
  getPrototypeNonEnumProps(obj) {
    return this._getPropertyNames(obj, false, true, this._notEnumerable);
  },
  getPrototypeProps(obj) {
    return this._getPropertyNames(
      obj,
      false,
      true,
      this._enumerableAndNotEnumerable,
    );
  },
  getOwnAndPrototypeEnumProps(obj) {
    return this._getPropertyNames(obj, true, true, this._enumerable);
    // Or could use unfiltered for...in
  },
  getOwnAndPrototypeNonEnumProps(obj) {
    return this._getPropertyNames(obj, true, true, this._notEnumerable);
  },
  getOwnAndPrototypeEnumAndNonEnumProps(obj) {
    return this._getPropertyNames(
      obj,
      true,
      true,
      this._enumerableAndNotEnumerable,
    );
  },
  // Private static property checker callbacks
  _enumerable(obj, prop) {
    return Object.prototype.propertyIsEnumerable.call(obj, prop);
  },
  _notEnumerable(obj, prop) {
    return !Object.prototype.propertyIsEnumerable.call(obj, prop);
  },
  _enumerableAndNotEnumerable(obj, prop) {
    return true;
  },
  // Inspired by http://stackoverflow.com/a/8024294/271577
  _getPropertyNames(obj, iterateSelf, iteratePrototype, shouldInclude) {
    const props = [];
    do {
      if (iterateSelf) {
        Object.getOwnPropertyNames(obj).forEach((prop) => {
          if (props.indexOf(prop) === -1 && shouldInclude(obj, prop)) {
            props.push(prop);
          }
        });
      }
      if (!iteratePrototype) {
        break;
      }
      iterateSelf = true;
      obj = Object.getPrototypeOf(obj);
    } while (obj);
    return props;
  },
};

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This page was last modified on Jul 8, 2025 by MDN contributors.

Querying object properties

Traversing object properties

Obtaining properties by enumerability/ownership

See also

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