ES2015 - Javascript For Modern Times

Slide 1

Slide 1 text

ES2015 Javascript For Modern Times   ES   JS + by Shai Mishali

Slide 2

Slide 2 text

Shai Mishali All-around geek. Mobile to Web to Backend. Constantly messing with new & weird technologies Winner of: BattleHack TLV 2014 BattleHack World Finals 2014 Ford TLV Developer Challenge 2015 freak4pc Shai Mishali

Slide 3

Slide 3 text

Agenda What are we gonna see today?

Slide 4

Slide 4 text

Agenda Tons of Code …

Slide 5

Slide 5 text

Agenda TONS OF MEMES !

Slide 6

Slide 6 text

A Bit of History ECMAScript?  JavaScript? What…?

Slide 7

Slide 7 text

A Bit of History • May 1995 - Brendan Eich, then an employee of Netscape, creates the first version of Javascript in just 10 days. • Originally named Mocha, then renamed to LiveScript, and eventually named JavaScript • ECMAScript is a standard specification. Javascript is merely a language implementing that standard (such as ActionScript) • ES1 - 1997, ES2 - 1998, ES3 - 1999, ES4 - 2000, ES5 - 2011, ES6/ES2015 - 2013

Slide 8

Slide 8 text

Let & Const Block-Scoped Fixes the Horrors of Hoisting

Slide 9

Slide 9 text

The Horrors of Hoisting y = 8 console.log(y) // Trying to run any of the following commands // without prior var will result in an error >> Uncaught ReferenceError: y is not defined >> Uncaught ReferenceError: y is not defined

Slide 10

Slide 10 text

// But, What do you think the following code will do ? console.log(y) var y = 8 The Horrors of Hoisting // Or even worse... this code ? y = 8 console.log(y + " " + x) var y var x = 4

Slide 11

Slide 11 text

>> undefined The Horrors of Hoisting // But, What do you think the following code will do ? console.log(y) var y = 8 // Or even worse... this code ? y = 8 console.log(y + " " + x) var y var x = 4 >> 8 undefined

Slide 12

Slide 12 text

The Horrors of Hoisting

Slide 13

Slide 13 text

// This: console.log(y) var y = 8 // And this: y = 8 console.log(y + "" + x) var y var x = 4 Prior to executing our code, Javascript moves our var declarations to the top of the scope. This is known as Hoisting. The Horrors of Hoisting

Slide 14

Slide 14 text

Prior to executing our code, Javascript moves our var declarations to the top of the scope. This is known as Hoisting. // This: console.log(y) var y = 8 // And this: y = 8 console.log(y + "" + x) var y var x = 4 // This: var y console.log(y) y = 8 // And this: var y, x y = 8 console.log(y) x = 4 Turns To The Horrors of Hoisting

Slide 15

Slide 15 text

This becomes even more unexpected and hazardous in loops. Take this simple for loop, for example The Horrors of Hoisting for(var i = 0; i < 4; i++){ setTimeout(function(){ console.log(i) }) } >> 0 1 2 3 // expected behaviour

Slide 16

Slide 16 text

Slide 17

Slide 17 text

The var in the loop is actually hoisted to the top of the loop, so all iterations of the loop use the same i ! The Horrors of Hoisting for(var i = 0; i < 4; i++){ setTimeout(function(){ console.log(i) }) } var i for(i = 0; i < 4; i++){ setTimeout(function(){ console.log(i) }) } // i = 4 and only then // setTimeout(s) execute

Slide 18

Slide 18 text

The Problem?

Slide 19

Slide 19 text

The Solution?

Slide 20

Slide 20 text

let variables are scoped to the nearest block and are NOT hoisted. var variables are scoped to the nearest function / global scope and ARE hoisted. Let is the new Var // lets are not hoisted so // y doesn't exist in first line y = 8 console.log(y) let y // let is block-scoped so y isn’t // visible in the second block // if this was a var, we would see "8" { let y = 8 } { console.log(y) }

Slide 21

Slide 21 text

Slide 22

Slide 22 text

This also solves our for loop issue. Each iteration of the loop is assigned its own i. Meaning, i is not shared across iterations. Let is the new Var for(let i = 0; i < 4; i++){ setTimeout(function(){ console.log(i) }) } >> 0 1 2 3 // expected behaviour let

Slide 23

Slide 23 text

Slide 24

Slide 24 text

Slide 25

Slide 25 text

Const const creates a read-only, block-scoped reference to a value. Commonly used as a magic-value holder. if(lessons.length > 20) { throw "Maximum Number of Lessons Exceeded" } const MAX_LESSONS = 20 if(lessons.length > MAX_LESSONS) { throw "Maximum Number of Lessons Exceeded" } // Constants require an initial value const MAX_LESSONS >> SyntaxError: missing = in const declaration // And can't be modified const MAX_STUDENTS = 500 MAX_STUDENTS = 350 // Silently ignored // They also can't be redeclared const MAX_STUDENTS = 500 const MAX_LESSONS = 20 const MAX_STUDENTS = 350 >> Uncaught TypeError: Identifier ‘MAX_STUDENTS' has already been declared constants require an initial value and can’t be redeclared

Slide 26

Slide 26 text

Let & Const

Slide 27

Slide 27 text

Rest & Spread Rest Parameters Spread Operator

Slide 28

Slide 28 text

Rest Parameters Lets say we have a setTags method on our User object that can accept any number of arguments (Variadic Function) User.setTags("music") User.setTags("music", "programming") User.setTags("music", "programming", "weightlifting") Nerdy  User Or Or

Slide 29

Slide 29 text

Usually we would use the arguments object, which is a built-in Array-like object containing the arguments of the function. Current Solution function setTags(){ for(let i in arguments){ console.log(arguments[i]) } } setTags("music", "programming") >> music programming

Slide 30

Slide 30 text

This technique works - but is very confusing and hard to read & maintain. Its really unclear where arguments come from and which arguments should the function accept. Current Solution function setTags(){ for(let i in arguments){ console.log(arguments[i]) } } setTags("music", "programming") >> music programming Where is this arguments var coming from? What should the function accept?

Slide 31

Slide 31 text

This technique also breaks easily which makes maintenance a nightmare. What if we need some other arguments in our function ? Current Solution function setTags(nickname, age){ for(let i in arguments){ console.log(arguments[i]) } } setTags("freak4pc", 28, "music", "programming") >> freak4pc 28 music programming

Slide 32

Slide 32 text

Slide 33

Slide 33 text

The Problem?

Slide 34

Slide 34 text

The Solution?

Slide 35

Slide 35 text

The new rest operator allows us to represent an indeﬁnite number of arguments as an Array which makes our code much more readable and less likely to break. Rest Parameters function setTags(nickname, age, ...tags){ for(let i in tags){ console.log(tags[i]) } } setTags("freak4pc", 28, "music", "programming")

Slide 36

Slide 36 text

Rest Parameters function setTags(nickname, age, ...tags){ for(let i in tags){ console.log(tags[i]) } } setTags("freak4pc", 28, "music", "programming") The REST of the arguments >> music programming The new rest operator allows us to represent an indeﬁnite number of arguments as an Array which makes our code much more readable and less likely to break.

Slide 37

Slide 37 text

Let’s say we want to take some data from an HTTP request and push it to our new User.setTags method Spread Operator API.getAllTags(function(data){ // data.tags is ["music", "programming"] User.setTags("freak4pc", 28, data.tags) })

Slide 38

Slide 38 text

Slide 39

Slide 39 text

The Solution?

Slide 40

Slide 40 text

The Spread operator lets us expand an expression where multiple arguments / elements are expected. Spread Operator API.getAllTags(function(data){ // data.tags is ["music", "programming"] User.setTags("freak4pc", 28, ...data.tags) })

Slide 41

Slide 41 text

Slide 42

Slide 42 text

Spread Operator We can use Spread for function calls, as well as array literals. Here are some sample usages: let adjs = ['pretty', 'awesome'] // No Spread let bad = ['spread', 'is', adjs, 'right?'] console.log(bad) >> spread, is, [pretty, awesome], right? >> spread, is, pretty, awesome, right? let adjs = ['pretty', 'awesome'] // With Spread let good = ['spread', 'is', ...adjs, 'right?'] console.log(good) let arr1 = ['all', 'your', 'items'] let arr2 = ['are', 'belong', 'to', 'us'] // No Spread arr1.push(arr2) >> all, your, items, [are, belong, to, us] let arr1 = ['all', 'your', 'items'] let arr2 = ['are', 'belong', 'to', 'us'] // With Spread arr1.push(...arr2) >> all, your, items, are, belong, to, us

Slide 43

Slide 43 text

Same same… but different The Spread operator and Rest parameters operator just look the same, but they are both used in different situations // Rest Parameters function setTags(...tags){ for(let i in tags){ let tag = tags[i] console.log(tag) } } Rest Parameters are used in function deﬁnitions Spread Operator is used in function invocations // Spread Parameters API.getAllTags(function(data){ User.setTags("shai", ...data.tags) }) … and array literals let adjs = ['pretty', 'awesome'] let are = ['spread', 'is', ...adjs, 'right?']

Slide 44

Slide 44 text

Rest & Spread

Slide 45

Slide 45 text

Arrow Functions Nicer Functions One-line functions Getting rid of bind() for scoping issues

Slide 46

Slide 46 text

Let’s examine the following piece of code processing an array of products. It will get the lowest price of a product within our price range. Function Gotchas - Syntax let products = [{"name": "MacBook", "price": 1299}, ...] let data = products .filter(function(p){ return p.price > 800 && p.price < 2000 }) // Filter products in prince range (800 to 2000) .map(function(p){ return p.price }) // Map just the price field to an Array .reduce(function(prev, curr){ return (prev < curr) ? prev : curr }) // Get the cheapest price in range

Slide 47

Slide 47 text

Notice how many times we have to repeat the function keyword, and how many blocks we have to create for just single-line functions. Function Gotchas - Syntax let products = [{"name": "MacBook", "price": 1299}, ...] let data = products .filter(function(p){ return p.price > 800 && p.price < 2000 }) // Filter products in prince range (800 to 2000) .map(function(p){ return p.price }) // Map just the price field to an Array .reduce(function(prev, curr){ return (prev < curr) ? prev : curr }) // Get the cheapest price in range

Slide 48

Slide 48 text

Slide 49

Slide 49 text

Regular functions also have some scoping issues when it comes to the this keyword. Let’s discuss this code using this in an internal scope. Function Gotchas - Scope let Shai = { x: 1, y: 2, go: function(){ setTimeout(function(){ console.log(this.y) }, 1000) } } Shai.go() >> Expected result : 2

Slide 50

Slide 50 text

Slide 51

Slide 51 text

Slide 52

Slide 52 text

Current solution consists on binding this to the lexical scope, which adds unneeded code, and is just plain ugly and unreadable (especially when needed often). Function Gotchas - Scope let Shai = { x: 1, y: 2, go: function(){ setTimeout(function(){ console.log(this.y) } } } Shai.go() >> Expected result : 2 .bind(this) , 1000)

Slide 53

Slide 53 text

Slide 54

Slide 54 text

The Problem?

Slide 55

Slide 55 text

The Solution?

Slide 56

Slide 56 text

Arrow Functions Arrow Functions have a shorter syntax compared to the regular function expressions. It also solves our scoping issues, as it always lexically binds ‘this’. API.getUser(function(data, err){ // Do stuff }) API.getUser((data, err) => { // Do stuff }) setTimeout(function(){ console.log("Timing Out!") }, 1000) setTimeout(() => { console.log("Timing Out!") }, 1000)

Slide 57

Slide 57 text

Arrow Functions We also get free one-line-functions for simple methods and also built-in lexical binding for ‘this’ (no more bind(), yay!) ['3', '5', '7'].map(function(n){ return n * n }) // YAY for one-liners ! \o/ ['3', '5', '7'].map(n => n * n) ['3', '5', ‘7’].map((n) => { return n * n; }) Or: setTimeout(function(){ console.log(this.x) }.bind(this), 1000) setTimeout(() => { console.log(this.x) }, 1000) // NO BIND, ‘this’ is lexically binded! One-line shorthand functions: Lexical ‘this’ binding:

Slide 58

Slide 58 text

Arrow Functions Lets wrap it all up with one big ﬁnal example. Let’s go back to our preview example with map, ﬁlter and reduce and start optimizing. let products = [{"name": "MacBook", "price": 1299}, ...] let data = products .filter( function( ){ return p.price > 800 && p.price < 2000 p }) .map( .reduce( function( ){ p return p.price }) function { }) return (prev < curr) ? prev : curr (prev, curr)

Slide 59

Slide 59 text

Arrow Functions Lets wrap it all up with one big ﬁnal example. Let’s go back to our preview example with map, ﬁlter and reduce and start optimizing. let products = [{"name": "MacBook", "price": 1299}, ...] let data = products .filter( p.price > 800 && p.price < 2000 p => .map( .reduce( ) p p.price (prev < curr) ? prev : curr (prev, curr) => ) 10 lines become 4 lines! Much Better :-) => )

Slide 60

Slide 60 text

Arrow Functions

Slide 61

Slide 61 text

Default Values Finally makes sense Scales Rather Easily No ugly y = y || undeﬁned

Slide 62

Slide 62 text

Default Values Having no default values for functions is quite the issue. Many unexpected results for both the user and the developer can occur… >> TypeError: Cannot read property 'length' of undefined No guarantee users will be an Array, or even deﬁned Also, looking at the function signature, it’s not clear which type users should be numberOfUsers() numberOfUsers(undefined) function numberOfUsers(users){ let size = users.length console.log(size) }

Slide 63

Slide 63 text

Default Values One of the current workarounds around this is checking for the presence of the argument in the beginning of a function function numberOfUsers(users){ let size = users.length console.log(size) } numberOfUsers() numberOfUsers(undefined) >> 0 // doesn’t break, falls back to [] users = users || [] Unfortunately, this option is too verbose, hard to maintain, and doesn’t scale well for many arguments function getClasses(user, city, date) { user = user || new User() city = city || "N/A" date = date || new Date() // etc ... // etc ... UGH!! }

Slide 64

Slide 64 text

Default Values Luckily, ES2015 ﬁnally introduced Default Values as part of the speciﬁcation, which makes our life much easier: function numberOfUsers(users = []){ let size = users.length console.log(size) } function getClasses(user = new User(), city = "N/A", date = new Date()){ // awesome code ... // more awesome code ... console.log(date); // [object Date] } users defaults to an empty Array, and it’s easy to know it expects one Date String User object numberOfUsers() // 0 numberOfUsers(undefined) // 0 default values could be of any type, which sort-of creates hinting for devs

Slide 65

Slide 65 text

Default Values

Slide 66

Slide 66 text

For Of A sane partner for for … in get values, not indexes

Slide 67

Slide 67 text

For Of Up until now, the only for iterator we had is for … in , which returns the indexes of the object, and NOT the values themselves let users = ['shai', 'elia', 'guy', 'roni', 'tom'] for(let item in users){ console.log(item) } >> Expected result : 'shai', 'elia', 'guy', 'roni', 'tom' >> Actual result : 0, 1, 2, 3, 4

Slide 68

Slide 68 text

For Of

Slide 69

Slide 69 text

For Of

Slide 70

Slide 70 text

For Of ECMAScript 2015 yet again to the rescue. Replacing in for of gives us the expected behaviour. let users = ['shai', 'elia', 'guy', 'roni', 'tom'] for(let item of users){ console.log(item) } >> Expected result : 'shai', 'elia', 'guy', 'roni', 'tom' >> Actual result : 'shai', 'elia', 'guy', 'roni', 'tom'

Slide 71

Slide 71 text

For Of

Slide 72

Slide 72 text

Template Literal Strings with Embedded expressions Supports Multiline Make ` , not ‘

Slide 73

Slide 73 text

Template Literal ES5 String templating is a painful subject since it’s very awkward and especially weird with Multi-lined strings. It looks pretty much like this ... let name = 'Shai', age = 28, lang = 'Javascript' console.log("My name is " + name + " (" + age + "). I love " + lang + "!") >> My name is Shai (28). I love Javascript! This is even icky-er with multi-line strings let id = 'divvy', content = 'Awesome Content!' let div = '

' + '

' + content + '

' + '

Slide 74

Slide 74 text

The Problem?

Slide 75

Slide 75 text

The Solution?

Slide 76

Slide 76 text

Template Literal In ES2015, Using a backtick ( ` ) instead of an apostrophe ( ‘ ) gives you inline embedded expressions using ${expression}, as well as multi-line support let name = 'Shai', age = 28, lang = 'Javascript' console.log(`My name is ${name} (${age}). I love ${lang}!`) >> My name is Shai (28). I love Javascript! Multi-line support is also substantially easier let id = 'divvy', content = 'Awesome Content!' let div = `

${content}

` No ugly + sign concatenation! Much more readable

Slide 77

Slide 77 text

Template Literal

Slide 78

Slide 78 text

Destructuring Split values from data structures Join value into data structures Return multiple values Similar to Tuple in Python/Swift

Slide 79

Slide 79 text

Destructuring Destructuring is a new assignment syntax allowing us to extract multiple pieces of data from Arrays and Objects. Very similar to Tuples in Python/Swift. let user = ['Shai Mishali’, ‘[email protected]', 'freak4pc'] // ES5 let name = user[0] let email = user[1] let github = user[2] We can also skip values if only some of them are needed let [name, , github] = user let user = ['Shai Mishali’, ‘[email protected]', ‘freak4pc'] // ES2015 Destructuring let [name, email, github] = user }

Slide 80

Slide 80 text

We can also use destructuring to return multiple values from a function, for example this function that returns a numbers’ Power of 2 and Square Root: function powAndSqrt(a){ return [Math.pow(a, 2), Math.sqrt(a)] } Now we want to take both values and print them out No Destructuring (ES5): With Destructuring: let result = powAndSqrt(9) let power = result[0] let root = result[1] let [power, root] = powAndSqrt(9) console.log(power) // 81 console.log(root) // 3 console.log(power) // 81 console.log(root) // 3 or an inline arrow function … let [power, root] = (a) => [Math.pow(a,2), Math.sqrt(a)] Destructuring

Slide 81

Slide 81 text

Deconstructing isn’t only for Arrays. It’s also extremely useable with Objects of most kinds. Let’s take a look at fetching data from document.location. What we would usually do would look like that Destructuring let location = document.location let {protocol, hostname, port} = location No Destructuring (ES5): With Destructuring: let location = document.location let protocol = location.protocol let hostname = location.hostname let port = location.port

Slide 82

Slide 82 text

Another cool thing we can use Object Destructuring for is loops: Destructuring No Destructuring (ES5): With Destructuring: for(let product of products){ let price = product.price let name = product.name console.log(`${name} : ${price}USD`) } for(let {price, name} of products){ console.log(`${name} : ${price}USD`) } This is applicable and really useful for arrays as well: No Destructuring (ES5): With Destructuring: for(let place of places){ let name = place.name let coords = place.coords let lat = coords[0] let lng = coords[1] console.log(`${name} at ${lat} by ${lng}`) } for(let {name, coords: [lat, lng]} of places){ console.log(`${name} at ${lat} by ${lng}`) } } }

Slide 83

Slide 83 text

Destructuring

Slide 84

Slide 84 text

Classes Javascript ﬁnally gets OOP ! Syntactic Sugar Allows Extending Classes Much Cleaner & Makes More Sense

Slide 85

Slide 85 text

Classes Up until today, creating a Class-like object consisted of a Function Expression. For example, this Product Class: function Product(title = "", model = ""){ this.title = title this.model = model this.getOrders = function(){ return ["OD23533", "OD11423", "OD72839"] } } let p = new Product("MacBook Pro", "MF83922/A") console.log(p) [object Object] { getOrders: function () { return ["OD23533", "OD11423", "OD72839"]; }, model: "MF83922/A", title: "MacBook Pro" } >>

Slide 86

Slide 86 text

Classes There are several issues with this method: function Product(title = "", model = ""){ this.title = title this.model = model this.getOrders = function(){ return ["OD23533", "OD11423", "OD72839"] } } let p = new Product("MacBook Pro", "MF83922/A") console.log(p) [object Object] { getOrders: function () { return ["OD23533", "OD11423", "OD72839"]; }, model: "MF83922/A", title: "MacBook Pro" } >> function doesn’t syntactically make sense as a Class No OOP Concepts such as constructor/getter/setter Inheritance is a big headache, only using __proto__

Slide 87

Slide 87 text

Classes

Slide 88

Slide 88 text

Classes ES2015 classes ﬁnally introduce actual OOP concepts into Javascript and allows actual syntactical meaning. Let’s transform our Product to a Class: class Product{ constructor(title = "", model = ""){ this.title = title this.model = model } getOrders(){ return ["OD23533", "OD11423", "OD72839"] } } let p = new Product("MacBook Pro", "MF83922/A") console.log(p.getOrders()) ["OD23533", "OD11423", "OD72839"]; >>

Slide 89

Slide 89 text

Classes Even though ES2015 Classes are purely syntactical sugar (meaning they base off function expressions and __proto__), we still get a much clearer syntax for even more complex abilities such a inheritance and getters: class Laptop extends Product{ constructor(title = "", model = "", price = 1000){ super(title, model) this.price = 1000 } get details(){ return `${this.title}, Model ${this.model} (${this.price}USD)` } } let l = new Laptop("MacBook Pro", "MF83922/A", 1400) console.log(l.details) MacBook Pro, Model MF83922/A (1000USD) >>

Slide 90

Slide 90 text

Classes

Slide 91

Slide 91 text

Other cool subjects We can’t have everything :-)

Slide 92

Slide 92 text

Other cool subjects • Promises • Generators • Modules • Proxy • Reflect Some other cool subjects we unfortunately don’t have time for today:

Slide 93

Slide 93 text

Use ES2015 Today! How do we get started?

Slide 94

Slide 94 text

Use ES2015 Today! Unfortunately, ES2015 is still not fully supported in all browsers. http://bit.ly/es6-compat-table

Slide 95

Slide 95 text

Use ES2015 Today! The best solution we have today is called Babel. Babel is a Transpiler - Translating ES2015 code to ES5, until ES2015 is fully compatible. It also provides a live REPL to test code online. (https://babeljs.io/repl/) https://babeljs.io

Slide 96

Slide 96 text

Thank You! Questions?   ES   JS +