Object

Overview

The Object type is used to store various keyed collections and more complex entities. Nearly all objects in JavaScript are instances of Object.

For more information see: Object (MDN).

Methods Summarized

Type	Name	Summary
Object	assign(target, sources)	Copy the values of all enumerable own properties from one or more source objects to a target object.
Object	create(object)	Creates a new object, using an existing object to provide the newly created object's prototype.
Object	create(object, properties)	Creates a new object, using an existing object to provide the newly created object's prototype and properties.
Object	defineProperties(object, properties)	Defines new or modifies existing properties directly on an object, returning the object.
Object	defineProperty(object, property, descriptor)	Allows a precise addition to or modification of a property on an object.
Array	entries(object1)	Returns an array whose elements are arrays corresponding to the enumerable string-keyed property key-value pairs found directly upon object.
Object	freeze(object)	Freezes an object: that is, prevents new properties from being added to it; prevents existing properties from being removed; and prevents existing properties, or their enumerability, configurability, or writability, from being changed.
Object	fromEntries(entries)	Transforms a list of key-value pairs into an object
Object	getOwnPropertyDescriptor(object, property)	Permits examination of the precise description of a property.
Array	getOwnPropertyNames(object)	Returns an array of all properties (including non-enumerable properties) found directly upon a given object.
Object	getPrototypeOf(object)	Returns the prototype of the specified object.
Boolean	hasOwnProperty(prop)	Determine whether the object has the specified property as its own property (as opposed to inheriting it).
Boolean	is(value1, value2)	Determines whether two values are the same value.
Boolean	isExtensible(object)	Determines if an object is extensible (whether it can have new properties added to it).
Boolean	isFrozen(object)	Determines if an object is frozen.
Boolean	isPrototypeOf(object)	Checks if an object exists in another object's prototype chain.
Boolean	isSealed(object)	Determines if an object is sealed.
Array	keys(object)	Returns an array of all own enumerable properties found upon a given object, in the same order as that provided by a for-in loop (the difference being that a for-in loop enumerates properties in the prototype chain as well).
Object	preventExtensions(object)	Prevents new properties from ever being added to an object (i.
Boolean	propertyIsEnumerable(prop)	Indicates whether the specified property is enumerable.
Object	seal(object)	Seals an object, preventing new properties from being added to it and marking all existing properties as non-configurable.
void	setPrototypeOf(obj, prototype)	Sets the prototype of a specified object to another object or null.
String	toLocaleString()	Returns a string representing the object.
String	toString()	Returns a string representing the specified object.
Object	valueOf()	Returns the primitive value of the specified object.
Array	values(object1)	Returns an array whose elements are strings corresponding to the enumerable string-keyed property values found directly upon object.

Methods Detailed

assign(target, sources)

Copy the values of all enumerable own properties from one or more source objects to a target object.

Parameters

• Object target The target object.
• Array sources The source object(s).

Returns: Object The target object.

Sample

var object1 = { a: 1, b: 2, c: 3};
var object2 = Object.assign({c: 4, d: 5}, object1);
application.output(object2.c, object2.d);

create(object)

Creates a new object, using an existing object to provide the newly created object's prototype.

Parameters

• Object object The object which should be the prototype of the newly-created object.

Returns: Object A new object with the specified prototype object.

Sample

const person = {
	isHuman: false,
	printIntroduction: function () {
		application.output("My name is " + this.name + ". Am I human? " + this.isHuman);
	}
};
var me = Object.create(person);
me.name = "Matthew"; // "name" is a property set on "me", but not on "person"
me.isHuman = true; // inherited properties can be overwritten
me.printIntroduction(); // expected output: "My name is Matthew. Am I human? true"

create(object, properties)

Creates a new object, using an existing object to provide the newly created object's prototype and properties.

Parameters

• Object object The object which should be the prototype of the newly-created object.
• Object properties ;

Returns: Object A new object with the specified prototype object.

Sample

var o = Object.create({}, { p: { value: 42 } });
application.output(o.p);

defineProperties(object, properties)

Defines new or modifies existing properties directly on an object, returning the object.

Parameters

• Object object The object on which to define or modify properties.
• Object properties An object whose own enumerable properties constitute descriptors for the properties to be defined or modified. Descriptors have the following keys: configurable - true if and only if the type of this property descriptor may be changed and if the property may be deleted from the corresponding object. Defaults to false. enumerable - true if and only if this property shows up during enumeration of the properties on the corresponding object. Defaults to false. value - The value associated with the property. Can be any valid JavaScript value (number, object, function, etc). Defaults to undefined. writable - true if and only if the value associated with the property may be changed with an assignment operator. Defaults to false. get - A function which serves as a getter for the property, or undefined if there is no getter. The function return will be used as the value of property. Defaults to undefined. set - A function which serves as a setter for the property, or undefined if there is no setter. The function will receive as only argument the new value being assigned to the property. Defaults to undefined.

Returns: Object The object that was passed to the function.

Sample

const object1 = {};
Object.defineProperties(object1, {property1: {value: 42, writable: true},   property2: {}});
application.output(object1.property1);

defineProperty(object, property, descriptor)

Allows a precise addition to or modification of a property on an object.

Parameters

• Object object The object on which to define or modify properties.
• Object property The name of the property to be defined or modified.
• Object descriptor The descriptor for the property being defined or modified.

Returns: Object The object that was passed to the function.

Sample

const object1 = {};
Object.defineProperty(object1, 'property1', {value: 42, writable: false});
application.output(object1.property1);

entries(object1)

Returns an array whose elements are arrays corresponding to the enumerable string-keyed property key-value pairs found directly upon object.

Parameters

• Object object1 An object.

Returns: Array An array of the given object's own enumerable string-keyed property key-value pairs. Each key-value pair is an array with two elements: the first element is the property key (which is always a string), and the second element is the property value.

Sample

const object1 = { a: 'somestring',  b: 42,  c: false};
application.output(Object.entries(object1));

freeze(object)

Freezes an object: that is, prevents new properties from being added to it; prevents existing properties from being removed; and prevents existing properties, or their enumerability, configurability, or writability, from being changed. In essence the object is made effectively immutable.

Parameters

• Object object The object to freeze.

Returns: Object The object that was passed to the function.

Sample

const object1 = { property1: 42 };
const object2 = Object.freeze(object1);
object2.property1 = 33;
application.output(object2.property1); //expected result is 42

fromEntries(entries)

Transforms a list of key-value pairs into an object

Parameters

• Array entries A list of objects. Each object is an array with two values, first value is the key second one is the value.

Returns: Object A new object whose properties are given by the entries of the array.

Sample

application.output(Object.fromEntries(entries));

getOwnPropertyDescriptor(object, property)

Permits examination of the precise description of a property.

Parameters

• Object object The object in which to look for the property.
• Object property The name of the property whose description is to be retrieved.

Returns: Object A property descriptor of the given property if it exists on the object, undefined otherwise.

Sample

const object1 = { property1: 42 };
const descriptor1 = Object.getOwnPropertyDescriptor(object1, 'property1');
application.output(descriptor1.configurable); // expected output: true
application.output(descriptor1.value); //expected result is 42

getOwnPropertyNames(object)

Returns an array of all properties (including non-enumerable properties) found directly upon a given object.

Parameters

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

Returns: Array An array of strings that correspond to the properties found directly upon the given object.

Sample

const object1 = { a: 1, b: 2, c: 3};
application.output(Object.getOwnPropertyNames(object1));

getPrototypeOf(object)

Returns the prototype of the specified object.

Parameters

• Object object The object whose prototype is to be returned.

Returns: Object The prototype of the given object. If there are no inherited properties, null is returned.

Sample

const prototype1 = {};
const object1 = Object.create(prototype1);
application.output(Object.getPrototypeOf(object1) === prototype1); // expected output: true

hasOwnProperty(prop)

Determine whether the object has the specified property as its own property (as opposed to inheriting it).

Parameters

• String prop The name of the property to test.

Returns: Boolean A Boolean indicating whether or not the object has the specified property as own property.

Sample

const object1 = new Object();
 object1.property1 = 42;
 application.output(object1.hasOwnProperty('property1')); // expected output: true
 application.output(object1.hasOwnProperty('toString')); // expected output: false
 application.output(object1.hasOwnProperty('hasOwnProperty')); // expected output: false

is(value1, value2)

Determines whether two values are the same value.

Parameters

• Object value1 The first value to compare.
• Object value2 The second value to compare.

Returns: Boolean a Boolean indicating whether or not the two arguments are the same value.

Sample

Object.is('foo', 'foo');

isExtensible(object)

Determines if an object is extensible (whether it can have new properties added to it). Objects are extensible by default, can be marked as non-extensible using Object.preventExtensions(), Object.seal(), or Object.freeze().

Parameters

• Object object The object which should be checked.

Returns: Boolean A Boolean indicating whether or not the given object is extensible.

Sample

var empty = {};
Object.isExtensible(empty); // === true

Object.preventExtensions(empty);
Object.isExtensible(empty); // === false

var sealed = Object.seal({});
Object.isExtensible(sealed); // === false

var frozen = Object.freeze({});
Object.isExtensible(frozen); // === false

isFrozen(object)

Determines if an object is frozen. An object is frozen if and only if it is not extensible, all its properties are non-configurable, and all its data properties (that is, properties which are not accessor properties with getter or setter components) are non-writable.

Parameters

• Object object The object which should be checked.

Returns: Boolean A Boolean indicating whether or not the given object is frozen.

Sample

const object1 = { property1: 42 };
application.output(Object.isFrozen(object1)); // expected output: false
Object.freeze(object1);
application.output(Object.isFrozen(object1)); // expected output: true

isPrototypeOf(object)

Checks if an object exists in another object's prototype chain.

Parameters

• Object object The object whose prototype chain will be searched.

Returns: Boolean A Boolean indicating whether the calling object lies in the prototype chain of the specified object.

Sample

function object1() {}
function object2() {}
object1.prototype = Object.create(object2.prototype);
const object3 = new object1();
application.output(object1.prototype.isPrototypeOf(object3)); // expected output: true
application.output(object2.prototype.isPrototypeOf(object3)); // expected output: true

isSealed(object)

Determines if an object is sealed. An object is sealed if it is not extensible and if all its properties are non-configurable and therefore not removable (but not necessarily non-writable).

Parameters

• Object object The object which should be checked.

Returns: Boolean A Boolean indicating whether or not the given object is sealed.

Sample

const object1 = { property1: 42 };
application.output(Object.isSealed(object1)); // expected output: false
Object.seal(object1);
application.output(Object.isSealed(object1)); // expected output: true

keys(object)

Returns an array of all own enumerable properties found upon a given object, in the same order as that provided by a for-in loop (the difference being that a for-in loop enumerates properties in the prototype chain as well).

Parameters

• Object object An array of strings that represent all the enumerable properties of the given object.

Returns: Array The object of which the enumerable's own properties are to be returned.

Sample

const object1 = {a: 'somestring', b: 42, c: false };
application.outout(Object.keys(object1)); // expected output: Array ["a", "b", "c"]

preventExtensions(object)

Prevents new properties from ever being added to an object (i.e. prevents future extensions to the object).

Parameters

• Object object The object which should be made non-extensible.

Returns: Object The object being made non-extensible.

Sample

const object1 = {};
Object.preventExtensions(object1);
try {
  Object.defineProperty(object1, 'property1', {
      value: 42
 });
 } catch (e) {
   application.output(e);
}

propertyIsEnumerable(prop)

Indicates whether the specified property is enumerable.

Parameters

• Object prop The name or symbol of the property to test.

Returns: Boolean A Boolean indicating whether the specified property is enumerable.

Sample

const array1 = [];
object1.property1 = 42;
array1[0] = 42;
application.output(object1.propertyIsEnumerable('property1')); // expected output: true
application.output(array1.propertyIsEnumerable(0)); // expected output: true
application.output(array1.propertyIsEnumerable('length')); // expected output: false

seal(object)

Seals an object, preventing new properties from being added to it and marking all existing properties as non-configurable. Values of present properties can still be changed as long as they are writable.

Parameters

• Object object The object which should be sealed.

Returns: Object The object being sealed.

Sample

const object1 = { property1: 42 };
Object.seal(object1);
object1.property1 = 33;
application.output(object1.property1); // expected output: 33

delete object1.property1; // cannot delete when sealed
application.output(object1.property1); // expected output: 33

setPrototypeOf(obj, prototype)

Sets the prototype of a specified object to another object or null.

Parameters

• Object obj The object which is to have its prototype set.
• Object prototype The object's new prototype (an object or null).

Returns: void

Sample

const obj = {};
const parent = { foo: 'bar' };

application.output(obj.foo);
// Expected output: undefined
Object.setPrototypeOf(obj, parent);
application.output(obj.foo);
// Expected output: "bar"

toLocaleString()

Returns a string representing the object. This method is meant to be overriden by derived objects for locale-specific purposes.

Returns: String A string representing the object.

Sample

const number1 = 123456.789;
application.output(number1.toLocaleString()); // expected output: "123.456,789"

toString()

Returns a string representing the specified object.

Returns: String A string representing the object.

Sample

function Dog(name) {
  this.name = name;
}
var dog1 = new Dog('Spike');
Dog.prototype.toString = function dogToString() { return this.name; }

application.output(dog1.toString());

valueOf()

Returns the primitive value of the specified object. By default, the valueOf method is inherited by every object descended from Object. Every built-in core object overrides this method to return an appropriate value. If an object has no primitive value, valueOf returns the object itself.

Returns: Object The primitive value of the specified object.

Sample

function MyNumberType(n) {
 this.number = n;
}
MyNumberType.prototype.valueOf = function() { return this.number; };

const object1 = new MyNumberType(4);
application.output(object1 + 3); // expected output: 7

values(object1)

Returns an array whose elements are strings corresponding to the enumerable string-keyed property values found directly upon object.

Parameters

• Object object1 An object.

Returns: Array an array of a given object's own enumerable string-keyed property values.

Sample

const object1 = { a: 'somestring',  b: 42,  c: false};
Object.values(object1);

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