A Crash Course to ES6
Why ES6?
Modules
Promises
Classes
Destructuring
And more!
But it's not in the browser yet...
Compile future JS to browser compliant JS
Fat Arrows
// declare another variable in higher scope
function Counter() {
this.time = 0;
var self = this;
setInterval(function() {
self.time++;
}, 1000);
}
// bind function to this
function Counter() {
this.time = 0;
setInterval(function() {
this.time++;
}.bind(this), 1000);
}
ES5
// lexical this with fat arrow
function Counter() {
this.time = 0;
setInterval(() => {
this.time++;
}, 1000);
}
ES6
function double(array) {
return array.map(function(item) {
return item * 2;
});
}
ES5
// fat arrow
function double(array) {
return array.map((item) => {
return item * 2;
});
}
// one liner with implicit return
function double(array) {
return array.map(item => item * 2);
}
ES6
Classes
function Animal(name) {
this.name = name;
}
Animal.prototype.sleep = function() {
console.log('zzZZ');
}
function Dog(name) {
}
Dog.prototype = new Animal();
var dog = new Dog();
dog.sleep(); // zzZZ
ES5
class Animal {
constructor(name) {
this.name = name;
}
sleep() {
console.log('zzZZ');
}
}
class Dog extends Animal {
}
var dog = new Dog();
dog.sleep(); // zzZZ
ES6
Destructuring
var object = {a: 2, b: 3, c: 4};
var a = object.a;
var b = object.b;
var c = object.c;
console.log(a, b, c); // 2 3 4
var array = ['a', 'b', 'c'];
var first = array[0];
var second = array[1];
var third = array[2];
console.log(first, second, third); // a b c
ES5
var object = {a: 2, b: 3, c: 4};
var {a, b, c} = object;
console.log(a, b, c); // 2 3 4
var array = ['a', 'b', 'c'];
var [first, second, third] = array;
console.log(first, second, third); // a b c
ES6
function pointLogger(point) {
var x = point.x;
var y = point.y;
console.log(x, y);
}
ES5
function pointLogger({x, y}) {
console.log(x, y);
}
ES6
Default/Rest/Spread
Parameters
function doStuff(arg1, arg2) {
if (arg1 === undefined) {
arg1 = 2;
}
if (arg3 === undefined) {
arg2 = 2;
}
console.log(arg1, arg2);
}
doStuff(3); // 3 4
ES5
function doStuff(arg1 = 2, arg3 = 4) {
console.log(arg1, arg2);
}
doStuff(3); // 3 4
ES6
Default Parameters
function log(first, ...rest) {
console.log(first, rest);
}
log(3); // 3 []
log(3, 2, 'more'); // 3 [2, 'more']
Rest Parameter
function sum(x, y, y) {
return x + y + z;
}
sum(...[1, 2, 3]); // 6
var obj1 = {a: 2, b: 3, c: 5};
var obj2 = {b: 4, d: 6};
var merged = {...obj1, ...obj2};
console.log(merged); // {a: 2, b: 4, c: 5, d: 6}
Spread Operator
Block Scope
function myFunc() {
var lexicalScope = 2;
if (lexicalScope === 2) {
let blockScope = 5;
console.log(blockScope, lexicalScope); // 5 2
}
console.log(blockScope, lexicalScope); // blockScope is not defined
}
let
const cantModifyMe = 2;
cantModifyMe = 4; // cantModifyMe is read-only
const
Modules
// helpers.js
export function func1() {}
export function func2() {}
export class Class1 {}
export var myVar = 2;
Named Exports
// main.js
import * as Helpers from 'helpers';
Helpers.func1();
Helpers.func2();
import {func1, func2} from 'helpers';
func1();
func2();
// helper.js
export default class Helper {
}
Default Export
// main.js
import Helper from 'helper';
var helper = new Helper();
import CallItSomethingElse from 'helper';
var anotherHelper = new CallItSomethingElse();
// helpers.js
export function func1() {}
export function func2() {}
export default class Class1 {}
export var myVar = 2;
Named and Default Exports
// main.js
import Class1, {func1, func2} from 'helpers';
func1();
func2();
var c = new Class1();
Promises
var promise = new Promise(function(resolve, reject) {
var data = asyncGetDataFromServer();
if (data.success) {
resolve(data.num);
}
else {
reject(Error('Server error'));
}
});
promise.then(function(result) {
console.log(result); // 5
}, function(error) {
console.log(error); // Error: 'Server error'
});
promise.then(function(result) {
console.log(result); // 5
}).catch(function(error) {
console.log(error); // Error: 'Server error'
});
or
promise.then(function(result) {
return result * 2; // 5 * 2
}).then(function(result) {
console.log(result); // 10
});
Promise.all([promise1, promise2, promise3]).then(function() {
// all resolved
}, function() {
// one or more promises failed
});
Template Strings
var myVariable = 50;
console.log(`This is my variable: ${myVariable}`);
// This is my variable: 50
Comparison to CoffeeScript
Similarities
- Fat arrow functions
- Classes
- Template strings
- Destructuring
class Animal
constructor: (@name) ->
move: (meters) ->
alert @name + " moved #{meters}m."
class Snake extends Animal
move: ->
alert "Slithering..."
super 5
sam = new Snake "Sammy the Python"
sam.move()
CoffeeScript
class Animal {
constructor(name) {
this.name = name;
}
move(meters) {
alert(`${this.name} moved ${meters}m.`);
}
}
class Snake extends Animal {
move() {
alert('Slithering...');
super.move(5);
}
}
var sam = new Snake('Sammy the Python');
sam.move();
ES6
Exercises
Get the broken code to function as expected by using ES6 features that solve these problems
Refactor the example to make use of ES6 features
Additional Resources
A Crash Course to ES6
By Jonathan Lehman
A Crash Course to ES6
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