The propertyIsEnumerable() method of Object instances returns a boolean indicating whether the specified property is this object's enumerable own property.

Try it

const object = {};
const array = [];
object.foo = 42;
array[0] = 42;

console.log(object.propertyIsEnumerable("foo"));
// Expected output: true

console.log(array.propertyIsEnumerable(0));
// Expected output: true

console.log(array.propertyIsEnumerable("length"));
// Expected output: false

Syntax

propertyIsEnumerable(prop)

Parameters

Return value

A boolean value indicating whether the specified property is enumerable and is the object's own property.

Description

All objects that inherit from Object.prototype (that is, all except null-prototype objects) inherit the propertyIsEnumerable() method. This method determines if the specified property, string or symbol, is an enumerable own property of the object. If the object does not have the specified property, this method returns false.

Examples

Using propertyIsEnumerable()

The following example shows the use of propertyIsEnumerable() on objects and arrays.

const o = {};
const a = [];
o.prop = "is enumerable";
a[0] = "is enumerable";

o.propertyIsEnumerable("prop"); // true
a.propertyIsEnumerable(0); // true

User-defined vs. built-in objects

Most built-in properties are non-enumerable by default, while user-created object properties are often enumerable, unless explicitly designated otherwise.

const a = ["is enumerable"];

a.propertyIsEnumerable(0); // true
a.propertyIsEnumerable("length"); // false

Math.propertyIsEnumerable("random"); // false
globalThis.propertyIsEnumerable("Math"); // false

Direct vs. inherited properties

Only enumerable own properties cause propertyIsEnumerable() to return true, although all enumerable properties, including inherited ones, are visited by the for...in loop.

const o1 = {
  enumerableInherited: "is enumerable",
};
Object.defineProperty(o1, "nonEnumerableInherited", {
  value: "is non-enumerable",
  enumerable: false,
});
const o2 = {
  // o1 is the prototype of o2
  __proto__: o1,
  enumerableOwn: "is enumerable",
};
Object.defineProperty(o2, "nonEnumerableOwn", {
  value: "is non-enumerable",
  enumerable: false,
});

o2.propertyIsEnumerable("enumerableInherited"); // false
o2.propertyIsEnumerable("nonEnumerableInherited"); // false
o2.propertyIsEnumerable("enumerableOwn"); // true
o2.propertyIsEnumerable("nonEnumerableOwn"); // false

Testing symbol properties

const sym = Symbol("enumerable");
const sym2 = Symbol("non-enumerable");
const o = {
  [sym]: "is enumerable",
};
Object.defineProperty(o, sym2, {
  value: "is non-enumerable",
  enumerable: false,
});

o.propertyIsEnumerable(sym); // true
o.propertyIsEnumerable(sym2); // false

Usage with null-prototype objects

Because null-prototype objects do not inherit from Object.prototype, they do not inherit the propertyIsEnumerable() method. You must call Object.prototype.propertyIsEnumerable with the object as this instead.

const o = {
  __proto__: null,
  enumerableOwn: "is enumerable",
};

o.propertyIsEnumerable("enumerableOwn"); // TypeError: o.propertyIsEnumerable is not a function
Object.prototype.propertyIsEnumerable.call(o, "enumerableOwn"); // true

Alternatively, you may use Object.getOwnPropertyDescriptor() instead, which also helps to distinguish between non-existent properties and actually non-enumerable properties.

const o = {
  __proto__: null,
  enumerableOwn: "is enumerable",
};

Object.getOwnPropertyDescriptor(o, "enumerableOwn")?.enumerable; // true
Object.getOwnPropertyDescriptor(o, "nonExistent")?.enumerable; // undefined

Object.prototype.propertyIsEnumerable()