Objects Flashcards
JS objects are simple collections of named … with ….
JavaScript objects are simple collections of named properties with values
JavaScript inheritance uses ….
Prototypes and a prototype chain, known as prototypal inheritance
Every object can have a reference to a … but it differs from the … on a …
Prototype, prototype property, function
We can define the prototype of an object by using the … method
Object.setPrototypeOf()
Every function has a …. property
Prototype property, not to be confused with the __proto__ / [[Prototype]] link on an object.
A function’s prototype property has a … property pointing back to itself
constructor
What is returned from the Person function?
function Person() {}
const x = new Person();
An object - an instance of the Person ‘class’.
The ES6 class syntax is really what under the hood?
Syntactic sugar for the constructor function / new keyword technique for prototypal inheritance
What does the super() call do?
It calls the parent class’s constructor function
Which of the following properties points to an object that will be searched if the target object doesn’t have the searched-for property?
- a class
- b instance
- c prototype
- d pointTo
c) prototype
After running the following code, what will ninja.constructor point to?
function Person() {}
function Ninja() {}
Ninja.prototype = new Person();
const ninja = new Ninja();
ninja.constructor will point to Person()
The Object.setPrototypeOf() method sets the … of a specified object to … or …
The Object.setPrototypeOf() method sets the prototype (i.e., the internal [[Prototype]] property) of a specified object to another object or null.
What are the parameters a & b in the following example?
Object.setPrototypeOf(a, b)
a: target object - the object which is to have its prototype set
b: prototype object - the object’s new prototype (an object or null)
What is the return value of Object.setPrototypeOf()?
The specified object that has its prototype changed
What is printed to the console?
const a = { speed: 100 };
const x = Object.setPrototypeOf({}, a);
console.log(x.speed);
100
How many parent object’s can the [[Prototype]] property hold?
1
The Object.create method creates a new …
Object
How many parameters does the Object.create() method take?
At least 1, the prototype object. There is also an optional properties object:
Object.create(proto[, propertiesObject])
What are the paramters a & b?
Object.create(a,b);
a: prototype object - the object that will be used as the prototype
b: properties object - an optional object
What is the return value of Object.create?
A new object with the specifed prototype object and properties
Can inheritance using Object.create be detected by instanceof? Why?
No. instanceof works by checking prototype constructors, and Object.create does not use constructors.
What can we use instead of instanceof to check prototypal inheritance using Object.create?
parentObject.isPrototypeOf(child) // boolean
Do objects have prototypes?
Yes
What is the difference between a function’s prototype and an object’s prototype?
All objects have a prototype, refered to by the __proto__ / chain property *. Functions are objects. Functions have prototypes.
However - this is confusing because there is a __proto__ (dunder proto) and an explicit .prototype property. Functions have both of these.
Foo.prototype is an explicit property of Foo:
Foo.prototype === Foo.__proto__ // false
[[Prototype]] is the actual object that is used in the prototypal lookup chain. Try to think of the underscores as being a chain __proto__ (the __proto__ is not supported by all engines).
* Objects can be created with their prototypes deliberately set to null, in which case searching their prototype returns undefined.
Does JavaScript have private object properties?
No.
Name 3 ways to mimic privacy within JavaScript
- ) Via closure
- ) Via Object.defineProperty creating setters & getters
- ) Via Symbols
