Object.prototype.propertyIsEnumerable()

Baseline Widely available

This feature is well established and works across many devices and browser versions. Itâs been available across browsers since 2015ë 7ì.

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const object1 = {};
const array1 = [];
object1.property1 = 42;
array1[0] = 42;

console.log(object1.propertyIsEnumerable("property1"));
// Expected output: true

console.log(array1.propertyIsEnumerable(0));
// Expected output: true

console.log(array1.propertyIsEnumerable("length"));
// Expected output: false

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obj.propertyIsEnumerable(prop);

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í¹ì ìì±ì´ ì´ê±°ê°ë¥íì§ ì¬ë¶ë¥¼ ëíë´ë Boolean.

ëª¨ë ê°ì²´ë propertyIsEnumerable ë©ìëë¥¼ ê°ì§ê³ ììµëë¤. ì´ ë©ìëë íë¡í íì ì²´ì¸ì íµí´ ììë í¹ì±ì ì ì¸íê³ ê°ì²´ì ì§ì ë ìì±ì for...in ë£¨íë¡ ì´ê±°í ì ìëì§ ì¬ë¶ë¥¼ íì¸í ì ììµëë¤. ê°ì²´ì ì§ì ë ìì±ì´ ìì¼ë©´ ì´ ë©ìëë falseë¥¼ ë°íí©ëë¤.

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A basic use of `propertyIsEnumerable`

The following example shows the use of propertyIsEnumerable on objects and arrays:

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

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

User-defined versus built-in objects

The following example demonstrates the enumerability of user-defined versus built-in properties:

var a = ["is enumerable"];

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

Math.propertyIsEnumerable("random"); // returns false
this.propertyIsEnumerable("Math"); // returns false

Direct versus inherited properties

var a = [];
a.propertyIsEnumerable("constructor"); // returns false

function firstConstructor() {
  this.property = "is not enumerable";
}

firstConstructor.prototype.firstMethod = function () {};

function secondConstructor() {
  this.method = function method() {
    return "is enumerable";
  };
}

secondConstructor.prototype = new firstConstructor();
secondConstructor.prototype.constructor = secondConstructor;

var o = new secondConstructor();
o.arbitraryProperty = "is enumerable";

o.propertyIsEnumerable("arbitraryProperty"); // returns true
o.propertyIsEnumerable("method"); // returns true
o.propertyIsEnumerable("property"); // returns false

o.property = "is enumerable";

o.propertyIsEnumerable("property"); // returns true

// These return false as they are on the prototype which
// propertyIsEnumerable does not consider (even though the last two
// are iteratable with for-in)
o.propertyIsEnumerable("prototype"); // returns false (as of JS 1.8.1/FF3.6)
o.propertyIsEnumerable("constructor"); // returns false
o.propertyIsEnumerable("firstMethod"); // returns false