Native Prototypes

Question 1

let obj = {};
alert( obj ); //

Answer 1

“[object Object]” ?

Question 2

obj = {} is the same as obj = new Object()

TRUE / FALSE

Answer 2

TRUE

Question 3

When new Object() is called (or a literal object {…} is created), the [[Prototype]] of it is set to ________

Answer 3

object.prototype

Question 4

when obj.toString() is called the method is taken from ____________

Answer 4

Object.prototype.

Question 5

let arr = [1, 2, 3];

// it inherits from Array.prototype?
alert( \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ ); // true

Answer 5

arr.__proto__ === Array.prototype

Question 6

let arr = [1, 2, 3];

// it inherits from Array.prototype?
alert( arr.\_\_proto\_\_ === Array.prototype ); // ?

Answer 6

true

Question 7

let arr = [1, 2, 3];

// then from Object.prototype?
alert( \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ ); // true

Answer 7

arr.__proto__.__proto__ === Object.prototype

Question 8

let arr = [1, 2, 3];

// then from Object.prototype?
alert( arr.\_\_proto\_\_.\_\_proto\_\_ === Object.prototype ); //

Answer 8

true

Question 9

let arr = [1, 2, 3];

// and null on the top.
alert( \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_); // null

Answer 9

arr.__proto__.__proto__.__proto__

Question 10

let arr = [1, 2, 3];

// and null on the top.
alert( arr.\_\_proto\_\_.\_\_proto\_\_ ); //

Answer 10

[[object Object]]

Question 11

function f() {}

alert(f.__proto__.__proto__ == Function.prototype); //

Answer 11

false

Question 12

function f() {}

alert(f.__proto__. == Function.prototype); //

Answer 12

true

Question 13

function f() {}

alert(f.__proto__.__proto__ == Object.prototype); //

Answer 13

true, inherit from objects

Question 14

Values _______ and _________ have no object wrappers

Answer 14

null

undefined

Question 15

_________ is a term for making a substitute for a method that exists in JavaScript specification, but not yet supported by current JavaScript engine

Answer 15

Polyfilling

Question 16

The __proto__ is considered outdated and somewhat deprecated (in browser-only part of the JavaScript standard).

The modern methods are:

Answer 16

Object.create(proto[, descriptors]) – creates an empty object with given proto as [[Prototype]] and optional property descriptors.

Object.getPrototypeOf(obj) – returns the [[Prototype]] of obj.

Object.setPrototypeOf(obj, proto) – sets the [[Prototype]] of obj to proto.

Question 17

Object.create(proto[, descriptors])

Does two things

Answer 17

1. creates a new object with assinged prototype

2. gives optional property descriptors. We can provide additional properties to the new object there

Question 18

// fully identical shallow clone of obj
let clone =

Answer 18

Object.create(Object.getPrototypeOf(obj), Object.getOwnPropertyDescriptors(obj));

Question 19

The __proto__ property is special: it must be either an _____ or _______

Answer 19

object

null

Question 20

__________ creates an empty object without a prototype

Answer 20

Object.create(null)

Question 21

function Rabbit(name) {
  this.name = name;
}
Rabbit.prototype.sayHi = function() {
  alert( this.name );
}

let rabbit = new Rabbit(“Rabbit”);

rabbit.sayHi(); //

Answer 21

Rabbit

Question 22

function Rabbit(name) {
  this.name = name;
}
Rabbit.prototype.sayHi = function() {
  alert( this.name );
}

let rabbit = new Rabbit(“Rabbit”);

Rabbit.prototype.sayHi(); //

Answer 22

undefined

Question 23

function Rabbit(name) {
  this.name = name;
}
Rabbit.prototype.sayHi = function() {
  alert( this.name );
}

let rabbit = new Rabbit(“Rabbit”);

Object.getPrototypeOf(rabbit).sayHi(); //

Answer 23

undefined

Question 24

function Rabbit(name) {
  this.name = name;
}
Rabbit.prototype.sayHi = function() {
  alert( this.name );
}

let rabbit = new Rabbit(“Rabbit”);

rabbit.__proto__.sayHi(); //

Answer 24

undefined

Question 25

The ________ method returns an array of a given object's own property names, in the same order as we get with a normal loop.

Answer 25

The Object.keys() method returns an array of a given object's own property names, in the same order as we get with a normal loop.

Question 26

``` const object1 = { a: 'somestring', b: 42, c: false }; ``` ``` console.log(Object.keys(object1)); // expected output: ```

Answer 26

Array ["a", "b", "c"]

Question 27

The _________method returns an array of a given object's own enumerable property values, 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).

Answer 27

The Object.values() method returns an array of a given object's own enumerable property values, 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).

Question 28

``` const object1 = { a: 'somestring', b: 42, c: false }; ``` ``` console.log(Object.values(object1)); // expected output: ```

Answer 28

Array ["somestring", 42, false]

Question 29

The _________method returns an array of a given object's own enumerable string-keyed property [key, value] pairs, 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).

Answer 29

The Object.entries() method returns an array of a given object's own enumerable string-keyed property [key, value] pairs, 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).

Question 30

``` const object1 = { a: 'somestring', b: 42 }; ``` for (let [key, value] of Object.entries(object1)) { console.log(`${key}: ${value}`); }

Answer 30

``` // "a: somestring" // "b: 42" // order is not guaranteed ```

Question 31

The ___________ method returns an array of all symbol properties found directly upon a given object.

Answer 31

The Object.getOwnPropertySymbols() method returns an array of all symbol properties found directly upon a given object.

Question 32

``` const object1 = { a: 1, b: 2, c: 3 }; ``` ``` console.log(Object.getOwnPropertyNames(object1)); // expected output: ```

Answer 32

Array ["a", "b", "c"]

Question 33

The ______________ method returns an array of all properties (including non-enumerable properties except for those which use Symbol) found directly in a given object.

Answer 33

The Object.getOwnPropertyNames() method returns an array of all properties (including non-enumerable properties except for those which use Symbol) found directly in a given object.

Question 34

The static _____________method returns an array of the target object's own property keys.

Answer 34

The static Reflect.ownKeys() method returns an array of the target object's own property keys.

Question 35

const object1 = { property1: 42, property2: 13 }; var array1 = []; ``` console.log(Reflect.ownKeys(object1)); // expected output: ```

Answer 35

Array ["property1", "property2"]

Question 36

const object1 = { property1: 42, property2: 13 }; var array1 = []; ``` console.log(Reflect.ownKeys(array1)); // expected output: ```

Answer 36

Array ["length"]

Question 37

The __________ method returns a boolean indicating whether the object has the specified property as its own property (as opposed to inheriting it).

Answer 37

The hasOwnProperty() method returns a boolean indicating whether the object has the specified property as its own property (as opposed to inheriting it).

Question 38

``` const object1 = new Object(); object1.property1 = 42; ``` ``` console.log(object1.hasOwnProperty('property1')); // expected output: ```

Answer 38

true

Question 39

``` const object1 = new Object(); object1.property1 = 42; ``` ``` console.log(object1.hasOwnProperty('toString')); // expected output: ```

Answer 39

false

Question 40

``` const object1 = new Object(); object1.property1 = 42; ``` ``` console.log(object1.hasOwnProperty('hasOwnProperty')); // expected output: ```

Answer 40

false