Upgrade to Pro
— share decks privately, control downloads, hide ads and more …
Speaker Deck
Features
Speaker Deck
PRO
Sign in
Sign up for free
Search
Search
Understanding JavaScript Prototypes
Search
sporto
August 11, 2013
Programming
3
330
Understanding JavaScript Prototypes
Also see
http://sporto.github.io/blog/2013/02/22/a-plain-english-guide-to-javascript-prototypes/
sporto
August 11, 2013
Tweet
Share
More Decks by sporto
See All by sporto
React inside Elm
sporto
2
180
Elm
sporto
1
250
Redux: Flux Reduced
sporto
1
330
Practically Immutable
sporto
0
180
Webpack and React
sporto
4
380
Rails with Webpack
sporto
1
210
Lesson learnt building Single Page Application
sporto
0
120
Grunt
sporto
1
170
Safe Testing in Ruby
sporto
1
120
Other Decks in Programming
See All in Programming
Носок на сок
bo0om
0
1.1k
KawaiiLT 登壇資料 キャリアとモチベーション
hiiragi
0
160
GitHub Copilot for Azureを使い倒したい
ymd65536
1
310
The New Developer Workflow: How AI Transforms Ideas into Code
danielsogl
0
110
Lambda(Python)の リファクタリングが好きなんです
komakichi
4
240
Dissecting and Reconstructing Ruby Syntactic Structures
ydah
3
2k
Browser and UI #2 HTML/ARIA
ken7253
2
170
REALITY コマンド作成チュートリアル
nishiuriraku
0
120
Thank you <💅>, What's the Next?
ahoxa
1
590
個人開発の学生アプリが企業譲渡されるまで
akidon0000
2
1.2k
KANNA Android の技術的課題と取り組み
watabee
0
190
Laravel × Clean Architecture
bumptakayuki
PRO
0
140
Featured
See All Featured
Helping Users Find Their Own Way: Creating Modern Search Experiences
danielanewman
29
2.6k
Keith and Marios Guide to Fast Websites
keithpitt
411
22k
How to Think Like a Performance Engineer
csswizardry
23
1.6k
How To Stay Up To Date on Web Technology
chriscoyier
790
250k
The Cult of Friendly URLs
andyhume
78
6.3k
Optimising Largest Contentful Paint
csswizardry
37
3.2k
It's Worth the Effort
3n
184
28k
The Illustrated Children's Guide to Kubernetes
chrisshort
48
49k
Making Projects Easy
brettharned
116
6.2k
We Have a Design System, Now What?
morganepeng
52
7.5k
Optimizing for Happiness
mojombo
378
70k
Git: the NoSQL Database
bkeepers
PRO
430
65k
Transcript
Understanding JS prototypes Sebastian Porto
+ Prototypes ! + Object.create ! + Constructor functions !
+ ES6
The wrong way to learn function Liquid() { } Liquid.prototype.fluid
= true; ! function Beer() { Liquid.call(this); } ! Beer.prototype = Object.create(Liquid.prototype); Beer.prototype.alcohol = 5.1; ! var beer = new Beer();
__proto__
• var liquid = {} var beer = {} •
beer.__proto__ = liquid A simple chain
A simple chain liquid beer __proto__ liquid is the prototype
of beer
Property look-ups • var liquid = { fluid: true }
• var beer = {} beer.__proto__ = liquid • beer.fluid //-> true
A simple chain liquid beer __proto__ fluid fluid? fluid?
A longer chain liquid coopers fluid fluid? beer drink
Long chain example • var liquid = { fluid: true
} • var drink = {} drink.__proto__ = liquid • var beer = {} beer.__proto__ = drink • var coopers = {} coopers.__proto__ = beer • coopers.fluid; //-> true
Many object can have same prototype liquid beer __proto__ cider
__proto__
Prototype can be shared • var liquid = { fluid:
true } • var beer = {} beer.__proto__ = liquid • var cider = {} cider.__proto__ = liquid • beer.fluid; //-> true cider.fluid; //-> true
Prototypes are not copies • var beer = { tasty:
true }; • var coopers = {}; coopers.__proto__ = beer; • coopers.tasty; //-> true • beer.tasty = false; • cooper.tasty; //-> false
beer coopers ethanol Prototypes are dynamic .__proto__
Prototypes are dynamic • var beer = { alcohol: 6
} var ethanol = { alcohol: 100 } • var coopers = {} coopers.__proto__ = beer • coopers.alcohol //-> 6 • coopers.__proto__ = ethanol • coopers.alcohol //-> 100
Writing creates properties • var beer = { alcohol: 6
} • var coopers = {} coopers.__proto__ = beer • coopers.alcohol = 4 • beer.alcohol //-> still 6
Creates ‘own’ property beer coopers alcohol = 6 .alcohol =
4 alcohol = 4 “own” property
beer coopers alcohol = 6 alcohol = 4 creatures Same
property can be in several places
Arrays • var beer = { ingredients: [‘wheat’, ‘yeast’]
} • var coopers = {} coopers.__proto__ = beer • coopers.ingredients.push(‘oats’) • beer.ingredients //->[‘wheat’, ‘yeast’, ‘oats’];
Direct modification beer coopers ingredients .ingredients.push(‘oats’)
coopers.ingredients.push(‘oats’); ! creatures.ingredients; //-> [‘wheat’, ‘yeast’, ‘oats’]; Arrays are modified
directly in the prototype beer coopers creatures ingredients ['wheat', 'yeast'] __proto__ __proto__
Objects are the same • var beer = {
ingredients: {wheat: 10, yeast: 20} } • var coopers = {} coopers.__proto__ = beer • coopers.ingredients.wheat = 30 • beer.ingredients.wheat //-> 30
__proto__ == great for learning ! Not for use
Object.create
Object.create • var beer = { tasty: true }
• var coopers = Object.create(beer) • coopers.tasty //-> true
Object.create var coopers = Object.create(beer); ! Just like: ! var
coopers = {}; coopers.__proto__ = beer;
Object.create is just setting __proto__ ! so same rules apply
- not copies - dynamic
getPrototypeOf var beer = { tasty: true }; ! var
coopers = Object.create(beer); ! ! Object.getPrototypeOf(coopers) //-> beer object
isPrototypeOf var beer = { tasty: true }; ! var
coopers = Object.create(beer); ! ! beer.isPrototypeOf(coopers); //-> true
ES6 setPrototypeOf var beer = { tasty: true }; !
var coopers = {}; ! ! Object.setPrototypeOf(coopers, beer);
Constructor Functions
Functions as constructors function Beer(){ ! } ! var beer
= new Beer(); Uppercase by convention
function Beer(){ ! ! ! ! ! } ! var
beer = new Beer(); Implicit this ! var this = {} this.__proto__ = Beer.prototype (yield to your code) return this
Implicit this function Beer(){ var this = {}; this.__proto__ =
Beer.prototype; this.tasty = true; return this; } ! var beer = new Beer(); ! beer.tasty; // true
function Beer(){ this.tasty = true; } ! var beer =
new Beer(); ! beer.tasty; //-> true Implicit this
Don’t forget new function Beer(){ this.kind = ‘beer’; } !
var beer = Beer(); this will the global object
function Beer(){ ! this.__proto__ = Beer.prototype; ! } function.prototype
function.prototype function Beer(){ ! } ! Beer.prototype Every function has
this special property
But this is not the prototype Beer.prototype !== Beer.__proto__ Call
this ‘function prototype’
function.prototype function Beer(){ ! } ! var beer = new
Beer(); beer.__proto__ ???? What is the __proto__ of beer?
It is assigned as the prototype of the instance function
Beer(){ var this = {}; this.__proto__ = Beer.prototype; this.tasty = true; return this; } It is assigned as the prototype of the new created object
Function instance new __proto__ Function prototype .prototype
• function Beer(){} • Beer.prototype.tasty = true • var coopers
= new Beer() • coopers.__proto__ == Beer.prototype //-> true • coopers.tasty //-> true It is the prototype assigned to the instance
function Beer(){ } ! Beer.prototype.brew = function () {} !
var coopers = new Beer(); var creatures = new Beer(); ! coopers.brew(); creatures.brew(); ! Useful for performance
• function Beer(){...} • Beer.prototype.ingredients = ['honey'] • var coopers
= new Beer() var vb = new Beer() • coopers.ingredients.push('oats') • vb.ingredients //-> ['honey', 'oats'] Again, same rules!
• function Beer(){ this.ingredients = [‘yeast’] } • var coopers
= new Beer() var creatures = new Beer() • coopers.ingredients.push(‘wheat’) • creatures.ingredients //-> [‘yeast’] Isolation
function Beer(){ ! } ! var coopers = new Beer();
! coopers instanceof Beer; //-> true ! instanceof
coopers instanceof Beer; ! ! Checks that ! coopers.__proto__ ==
Beer.prototype ! instanceof
var Beer = function () { ! }; ! Beer.findAll
= function () { ... } ! Beer.findAll(); "Class methods"
ES6
class Beer { constructor(a) { this.alcohol = a; } !
drink() { ... } } ES6 Classes
ES6 Classes function Beer(a){ this.alcohol = a; } ! Beer.prototype.drink
= function () { ... } ! var beer = new Beer(5) class Beer { constructor(a) { this.alcohol = a; } ! drink() { ... } } ! var beer = new Beer(5)
Questions? Thanks