adding es6 to your developer toolbox

#devES6ADDING ES6 TO YOUR TOOLBOX

@ j e f f re y s t r au s s

”ES6? That's the new JavaScript!

~ mr. developer

”No!

~ me

ECMAScript

ECMAScript2015

not all-or-nothingexperimentES6 IS AN EVOLUTION

experimentNOT ALL-OR-NOTHING

strings

template literals

var greeting =

"Hello, " + user.first + " " + user.last + "!";

var url =

"www.mysite.com" + "/foo/" + fooId + "/bar/" + barId;

ES5:

`backticks`

${expression}

multi-line strings

var poem = "so much depends\n"

+ "upon\n\n"

+ "a red wheel\n"

+ "barrow\n\n"

+ "glazed with rain\n"

+ "water\n\n"

+ "beside the white\n"

+ "chickens";

ES5:

var poem =

`so much depends

upon

a red wheel

barrow

glazed with rain

water

beside the white

chickens`;

ES6:

default parameters

var drawRect = function(width, height, color) {

width = width || 1;

height = height || 1;

color = color || 'orange';

/* draw stuff */

return width * height;

};

ES5:

var drawRect = function(width, height, color) {

width = width || 1;

height = height || 1;

color = color || 'orange';

/* draw stuff */


};

drawRect(); // draws orange; returns 1

drawRect(0, 4, 'blue'); // draws blue, but returns 4

ES5:

var drawRect = function(width=1, height=1, color='orange') { /* draw stuff */


};

ES6:

var drawRect = function(width=1, height=1, color='orange') { /* draw stuff */


};

drawRect(0, 4, 'blue'); // returns 0

ES6:

collections

arrays

var myStringArray = new Array("blue");

// ["blue"]

var myBoolArray = new Array(false);

// [false]

var myIntArray = new Array(2);

// [undefined x 2]

ES5:

var myIntArray = new Array(2);

// [undefined x 2]

ES5:

var fixedIntArray = Array.of(2); // [2]

ES6:

function getArgsArray() {

return Array.prototype.slice.apply(arguments);

};

getArgsArray('foo', true, 42);

// ['foo', true, 42]

ES5:


return Array.prototype.slice.apply(arguments);

};


// ['foo', true, 42]

ES5:


return Array.from(arguments); };


// ['foo', true, 42]

ES6:

iterables

`for-of` loop

var body = ['head', 'shoulders', 'knees', 'toes'];

for (var i = 0; i < body.length; i++) { tap(body[i]) };

ES5:


for (var i = 0; i < body.length; i++) { tap(body[i]) };

ES5:


for (var part of body) { tap(part);

}

ES6:

var alphabet = 'abcdefg';

for (var letter of alphabet) {

sing(letter);

}

ES6:

ES6:

...spread operator

var alphabet = 'abcdefg';

function sing() {

console.log(arguments);

}

sing(...alphabet); // ["a", "b", "c", "d", "e", "f", "g"]

ES6:

ES6:

destructuring

[ ] = fooArray;

{ } = fooObject;

var x, y, z, coords;

coords = [29, 22, 37];

x = coords[0];

y = coords[1];

z = coords[2];

ES5:


coords = [29, 22, 37];

x = coords[0];

y = coords[1];

z = coords[2];

ES5:

var coords = [29, 22, 37];

var [x, y, z] = coords;

ES6:


coords = [29, 22, 37];

x = coords[0];

y = coords[1];

z = coords[2];

ES5:

var coords = [29, 22, 37];

var [x, y, z] = coords; var [foo, , bar] = coords;

ES6:

var user, email, display;

user = { name: 'Jeff', email: '[email protected]' };

email = user.email;

display = user.name;

ES5:

var user, email, display;

user = { name: 'Jeff', email: '[email protected]' };

email = user.email;

display = user.name;

ES5:

var user = { name: 'Jeff', email: '[email protected]' };

var {email} = user; var {name: display} = user;

ES6:

swapping variables

var temp = x;

x = y;

y = temp;

ES5:

[y, x] = [x, y];

ES6:

process return values

var drawRect = function(width=1, height=1, color='orange') {

/* draw stuff */

return {area: width * height, hex: getHex(color)};

};

ES6:

{ scope }

block-scoped vars

function-scoped

var foo = function(bar) {

if (bar) {

var message = 'Hello!'; // declared here

alert(message);

}

return message; // still in scope here };

ES5:

iifeIMMEDIATELY INVOKED FUNCTION EXPRESSION

var foo = function(bar) {

if (bar) {

(function() { var message = 'Hello!'; // declared here

alert(message);

})(); }

return message; // ReferenceError: message is not defined };

ES5:

closure

// assume links has an array of DOM elements

for (var i = 0; i < links.length; i++) {

links[i].onclick = function() {

console.log(i);

};

}

// whoops! all links log the max index!

ES5:



links[i].onclick = (function(x) { return function() { console.log(x); // preserved context }; })(i); }

// clicking links gives the correct result

ES5:

hoisting & globals

function foo() {

x = 10;

y = 20;

var x, y;

var area = x * y;

return area;

};

ES5:

function foo() {

var x, y;

var area;

x = 10;

y = 20;

area = x * y;

return area;

};

ES5:

function foo() {

var x, y;

// yikes! area may be in the global scope!

x = 10;

y = 20;

area = x * y;

return area;

};

ES5:

function(bar) {

if (bar) {

var message = 'Hello!'; // declared here

alert(message);

}

return message; // still in scope here };

ES5:

function(bar) {

if (bar) {

let message = 'Hello!'; // declared here alert(message);

}

return message; // ReferenceError: message is not defined };

ES6:



links[i].onclick = function() {

console.log(i);

};

};

// whoops! all links log the max index!

ES5:


for (let i = 0; i < links.length; i++) { links[i].onclick = function() {

console.log(i);

};

};

// all better, with no IIFE or extra closure!

ES6:

temporal dead zone

function foo() {

x = 10; // ReferenceError: x is not defined

y = 20;

let x, y; let area = x * y;

return area;

};

ES6:

arrow functions

syntax

(args) => { statements }

function logSum(x, y) {

var sum = x + y;

console.log(sum);

}

ES5:

function logSum(x, y) {

var sum = x + y;

console.log(sum);

}

ES5:

let logSum = (a, b) => { let sum = a + b;

console.log(sum);

};

ES6:

(args) => expression;

function sum(x, y) {

return x + y;

}

ES5:

let sum = (x, y) => x + y;ES6:

let speak = () => 'Hello!';

let wrappedMethod = (arg) => innerMethod(arg);

let announce = (name) => `Announcing ${name}!`;

let getUser = () => ( { id: 42, name: 'Jeff' } );

ES6:



let announce = name => `Announcing ${name}!`;


ES6:



let announce = (name) => `Announcing ${name}!`;


ES6:

lexical `this`

var person = {

name: 'Jeff',

greet: function() {

console.log('Now greeting ' + this.name);

setTimeout(function() {

console.log('Hello, ' + this.name + '!');

}, 3000);

}

};

ES5:

var person = {

name: 'Jeff',

greet: function() {



console.log('Hello, ' + this.name + '!'); }, 3000);

}

};

person.greet();

// Now greeting Jeff

// Hello, !

ES5:

that | self

{ }.bind(this)

var person = {

name: 'Jeff',

greet: function() {


var that = this; setTimeout(function() {

console.log('Hello, ' + that.name + '!'); }, 3000);

}

};

ES5:

var person = {

name: 'Jeff',

greet: function() {



console.log('Hello, ' + this.name + '!'); }.bind(this), 3000); }

};

ES5:

let person = {

name: 'Jeff',

greet: function() {

console.log(`Greeting ${this.name}`);

setTimeout(() => { console.log(`Hello, ${this.name}!`);

}, 3000);

}

};

ES6:

putting it to use

compatibility

http://kangax.github.io

/compat-table/es6

bit.ly/es6-compat

$ npm install --save-dev babel-cli

$ npm install --save-dev babel-preset-es2015

$ echo '{ "presets": ["es2015"] }' > .babelrc

$ babel mySource.js -o myTranspiled.js

flexibility

babeljs.io/repl

not all-or-nothingNEXT STEPS

es6 is an evolution

evolve

@je f f re yS t r au s s #de vES6

[email protected]

adding es6 to your developer toolbox

Software