Js in the open

JS in the open
(or JS in the wild)

Friday, November 9, 12

@victorporof
Programmer at Mozilla


The JavaScript you probably know


Number

String

Boolean

Object (Function, Array, Date, RegExp ...)

Function

Null

Undefined


typeof 3 == “number”

typeof “Gangnam Style” == “string”

typeof false == “boolean”

typeof document == “object”

typeof document.getElementById == “object”

typeof null == “object”

typeof undefined == “undefined”


new Number(3)

new String(“Gangnam Style”)

new Boolean(false)


typeof new Number(3) == “object”

typeof new String(“Gangnam Style”) == “object”

typeof new Boolean(false) == “object”


typeof new Number(3) == “object”

typeof new String(“Gangnam Style”) == “object”

typeof new Boolean(false) == “object”

Constructors


JavaScript is fundamentally about Objects


The JavaScript you probably don’t know


new in JavaScript 1.6
2006

Functional collectors

Array extras

Array and String generics

for each..in loops



every(), filter(), forEach(), map(), some()

function isBigEnough(element, index, array) {
return (element >= 10);
}

var passed = [12, 5, 8, 130, 44].every(isBigEnough);
// passed is false

var passed = [12, 54, 18, 130, 44].every(isBigEnough);
// passed is true



every(), filter(), forEach(), map(), some()

function fuzzyPlural(single) {
var result = single.replace(/o/g, 'e');
return result;
}

var words = ["foot", "goose", "moose", "kangaroo"];
console.log(words.map(fuzzyPlural));

// ["feet", "geese", "meese", "kangaree"]


Array extras

indexOf(), lastIndexOf()

var array = [2, 5, 9, 2];
var index = array.lastIndexOf(2);
// index is 3
index = array.lastIndexOf(7);
// index is -1
index = array.lastIndexOf(2, 3);
// index is 3
index = array.lastIndexOf(2, 2);
// index is 0
index = array.lastIndexOf(2, -1);
// index is 3


Array and String generics

function isLetter(character) {
return (character >= "a" && character <= "z");
}

if (Array.prototype.every.call(str, isLetter)) {
alert("The string '" + str + "' contains only letters!");
}


for each..in loops

var sum = 0;
var obj = { prop1: 5, prop2: 13, prop3: 8 };

for (var item in obj) {
sum += item;
}
print(sum); // prints 0prop1prop2prop3


for each..in loops

var sum = 0;
var obj = { prop1: 5, prop2: 13, prop3: 8 };

for each (var item in obj) {
sum += item;
}
print(sum); // prints "26", which is 5+13+8


2007

Generators

Iterators

Array comprehensions

let statements, expressions, definitions

destructuring assignment

multiple value returns & looping across objects


Generators

function fib() {
var i = 0, j = 1;
while (true) {
yield i;
var t = i;
i = j;
j += t;
}
}

var g = fib();
for (var i = 0; i < 10; i++) {
console.log(g.next());
}


Iterators
var obj = {
name: "Jack Bauer",
username: "JackB",
id: 12345,
agency: "CTU",
region: "Los Angeles"
};

obj.__iterator__ = function() {
for (let item in this) {
if (item != "id") { yield this[item]; }
}
};

for (let item in obj) {
alert(item);
}


Array comprehensions

function range(begin, end) {
for (let i = begin; i < end; ++i) {
yield i;
}
}

var ten_squares = [i * i for each (i in range(0, 10))];

var evens = [i for each (i in range(0, 21)) if (i % 2 == 0)];


let definitions

for (var i = 0; i < 10; i++) {
console.log(i); // prints 0, 1, 2 ... 9
}
console.log(i); // prints 10

for (let i = 10; i < 100; i++) {
console.log(i); // prints 10, 11, 12 ... 99
}
console.log(i); // prints 10


let definitions
function varTest() {
var x = 31;
if (true) {
var x = 71; // same variable!
alert(x); // 71
}
alert(x); // 71
}

function letTest() {
let x = 31;
if (true) {
let x = 71; // different variable
alert(x); // 71
}
alert(x); // 31
}


let statements and expressions

var x = 5;
var y = 0;

let (x = x + 10, y = 12) {
console.log(x + y); // 15 + 12 = 27
}
console.log(x + y); // 5 + 0 = 5

var x = 5;
var y = 0;
console.log(let (x = x + 10, y = 12) x + y); // 15 + 12 = 27
console.log(x + y); // 5 + 0 = 5



var array = [1, 2, 3];
var [fir, sec, thi] = array; // fir = 1, sec = 2, thi = 3
var [, x] = array; // x = 2

var obj = {
name: "Jack Bauer",
username: "JackB",
id: 12345,
agency: "CTU",
};
var [name, agency, region] = obj;
// name = "Jack Bauer", agency = "CTU", region = "Los Angeles"



var a = 1;
var b = 3;

[a, b] = [b, a];


multiple value returns

function f() {
return [1, 2];
}

var [a, b] = f();
console.log("A is " + a + " B is " + b);


multiple value returns

function f() {
return { a: 1, b: 3 };
}

var [a, b] = f();
console.log("A is " + a + " B is " + b);


looping across objects
var obj = {
name: "Jack Bauer",
username: "JackB",
id: 12345,
agency: "CTU",
};

obj.__iterator__ = function() {
for (let item in this) {
if (item != "id") { yield [item, this[item]]; }
}
};

for (let [item, value] in obj) {
alert(item + ": " + value);
}


2008

expression closures

getters and setters

generator expressions

more Array extras


expression closures

function(x) { return x * x; }
// vs.
function(x) x * x

var passed = [12, 5, 8, 130, 44].every(function(e) e >= 10);
// passed is false

var passed = [12, 54, 18, 130, 44].every(function(e) e >= 10);
// passed is true


expression closures

(short function syntax, strawman)

function(x) { return x * x; }
// vs.
ƒ(x) x * x

[12, 5, 8, 130, 44].map(ƒ(e) e / 2);
// divide all values by 2

[12, 54, 18, 130, 44].map(ƒ(e) e % 2 ? true : false );
// map odds and evens


getters and setters

var object = {
_a: 7,
get a() { return this._a + 1; },
set a(x) { this._a = x / 2; }
};


getters and setters

var object = {
_a: 7,
get a() this._a + 1,
set a(x) this._a = x / 2
};



let it = (i + 3 for (i of [1, 2, 3]));

try {
while (true) {
alert(it.next());
}
} catch (err if err instanceof StopIteration) {
alert("End of record.");
}


more Array extras

reduce(), reduceRight()

var total = [0, 1, 2, 3].reduce(function(a, b) {
return a + b;
});
// total == 6


more Array extras

reduce(), reduceRight()

var total = [0, 1, 2, 3].reduce(function(a, b) a + b);


ES5 to ES6 and beyond
2009 ... ?

nicer Object API

default function params, rest params

for..of loops

WeakMaps, Maps, Sets

strict mode


Nicer Object API
var obj1 = {
name: "Jack Bauer",
username: "JackB",
id: 12345,
agency: "CTU",
};

var obj2 = Object.create(obj1, {
foo: {
value: "hello",
writable: true, // value may be changed
configurable: true // property may be changed or deleted
},
bar: {
enumerable: false, // shows up during enumeration
get: function() { return 10 },
set: function(value) { alert("Setting 'o.bar' to", value);
}
});


Nicer Object API
// Shape - class
function Shape() { // Shape constructor
this.x = 0;
this.y = 0;
}
Shape.prototype.move = function() {
this.x += 10;
this.y += 10;
console.info("Shape moved.");
};

var shape = new Shape(); // instantiate
shape.move(); // "Shape moved."


Nicer Object API
// Shape - superclass
this.x = 0;
this.y = 0;
}
this.x += 10;
this.y += 10;
};

// Rectangle - subclass
function Rectangle() { // Rectangle constructor
Shape.call(this); // call super constructor
}
Rectangle.prototype = Object.create(Shape.prototype); // inherit methods
Rectangle.prototype.moveAt = function(x, y) { // define new methods
this.x += x;
this.y += y;
console.info("Shape moved at: " + x + ", " + y);
};

var rect = new Rectangle(); // instantiate
rect instanceof Rectangle // true
rect.move(); // "Shape moved."
rect.moveAt(5, 2); // "Shape moved at: 5, 2"


Default and rest params
// when called, if no value or undefined is passed as second argument,
// b will have 1 as value.
function multiply(a, b = 1) {
return a * b;
}
multiply(5); // 5

function fun(a, b, ...theArgs) {
for (let arg of theArgs) console.log(arg);
}
fun(1, 2);
fun(1, 2, 5); // logs 5
fun(1, 2, 5, 6, 7); // logs 5, 6, 7

function sortRestArgs(x, ...someStuff) {
return someStuff.sort();
}
console.log(sortRestArgs(0, 5, 3, 7, 1)); // logs 1, 3, 5, 7


for..of loops
let arr = [ 3, 5, 7 ];
arr.foo = "hello";

for (let i in arr) {
console.log(i); // logs "0", "1", "2", "foo"
}

for (let i of arr) {
console.log(i); // logs "3", "5", "7"
}

for (let paragraph of document.querySelectorAll("article > p")) {
paragraph.classList.add("read");
}


Sets
// Sets are collections in which values are unique.
var mySet = new Set();

mySet.add(1);
mySet.add(5);
mySet.add("some text");

mySet.has(1); // true
mySet.has(3); // false, 3 has not been added to the set
mySet.has(5); // true
mySet.has(Math.sqrt(25)); // true
mySet.has("Some Text".toLowerCase()); // true
mySet.size; // 3

mySet.delete(5); // removes 5 from the set
mySet.has(5); // false, 5 has been removed
mySet.size; // 2, we just removed one value

// iterate over items in set
for (let item of mySet) console.log(item);
// logs the items in the order: 1, "some text"

// convert set to plain Array
var myArr = [v for (v of mySet)]; // [1, "some text"]


Maps vs. Weak Maps
// Maps are key/value collections in which keys are objects.
var myMap = new Map();

// setting the values
myMap.set(keyString, "value associated with 'a string'");
myMap.set(keyObj, "value associated with keyObj");
myMap.set(keyFunc, "value associated with keyFunc");

myMap.size; // 3

// getting the values
myMap.get(keyString); // "value associated with 'a string'"
myMap.get(keyObj); // "value associated with keyObj"
myMap.get(keyFunc); // "value associated with keyFunc"
myMap.get("a string"); // "value associated with 'a string'"

myMap.set(0, "positive zero");
myMap.get(-0); // "negative zero"

myMap.set(-0, "negative zero");
myMap.get(0); // "positive zero"

// iterate over items in map
for (let [key, value] of mySet) console.log(value);


Strict mode
"use strict";

mistypedVariable = 17;
// throws a ReferenceError

delete Object.prototype;
// throws a TypeError

var f = function() { return arguments.callee; };
f(); // throws a TypeError

var o = { p: 1, p: 2 };
// syntax error

function sum(a, a, c) { return a + a + c; }
// syntax error

function that() { return this; }
that(); // undefined


Harmony vs. Strawman
in a galaxy far far away ...

quasi-literals

thin and fat arrow functions with lexical this binding

triangle operator

modules

classes

ParallelArray


Paren-free
in a galaxy far far away ...

if year > 2010 {
syntax++
}

for i in iter {
frob(i)
}

while lo <= hi {
let mid = (lo + hi) / 2
}

... return [i * i for i in range(n)]


Rhino Unicorn

https://brendaneich.com/


https://brendaneich.com/


Design patterns


We won’t talk about design patters


avoid defensive programming
premature optimization is evil
over-complicating things is eviler
over-engineering is the evilest


What we use at Mozilla


What we use at Mozilla
and you should too


OOP
MyNamespace.Fox = function() {
this.name = "";
this.yearsOld = 0;
};

MyNamespace.Fox.prototype = {
run: function(param) {
},
sleep: function() {
}
};

var pinky = new Fox();
var leyla = new Fox();
leyla.cuteness = 5;


OOP
MyNamespace.Fox = function(aName, aYearsOld) {
this.name = aName;
this.yearsOld = aYearsOld;
};

MyNamespace.Fox.prototype = { constructors!
},
sleep: function() {
}
};

var pinky = new Fox("Pinky", 10);
var leyla = new Fox("Leyla", 7);
leyla.cuteness = 5;


OOP
this.name = aName;
};

MyNamespace.Fox.prototype = { private members?
},
sleep: function() {
}
};

leyla.cuteness = 5;


Closures!
function foo(a, b){
function bar() {
return a + b;
}

return bar();
}

function foo2(a, b){
function bar(c) {
return a + b + c;
}

return bar;
}


Closures!
function foo(a, b){
function bar() {
return a + b;
}
var res1 = foo(5, 2);
return bar();
}
var res2 = foo2(5, 2);
function bar(c) { var res3 = res2(3);
return a + b + c;
}

return bar;
}


Closures!
function foo(a, b){
function bar() {
return a + b;
}
var res1 = foo(5, 2);
return bar(); // returns 7
}
var res2 = foo2(5, 2);
// returns a closure function
function bar(c) { var res3 = res2(3);
return a + b + c; // returns 7
}

return bar;
}


OOP
this.name = aName;
};

}, private members?
sleep: function() {
}
};

leyla.cuteness = 5;

leyla.yearsOld; // 7


OOP
this._name = aName;
this._yearsOld = aYearsOld;
};

}, we just _preﬁx them
sleep: function() {
} ...and respect it
};

leyla.cuteness = 5;

leyla._yearsOld; // 7


OOP
var name = aName;
var yearsOld = aYearsOld;

this.run = function(param) {
};
this.sleep = function() {
}; you can have private members
};
...if you really want to
leyla.cuteness = 5;

leyla.yearsOld; // undefined


OOP
var name = aName;
var yearsOld = aYearsOld;

this.run = function(param) {
};
this.sleep = function() {
};
Object.defineProperty(this, "yearsOld", {
get: function() { return yearsOld * 6; }
set: function(value) { yearsOld = value; }
});
};

leyla.cuteness = 5;

leyla.yearsOld; // 42


OOP
// Shape - superclass
this.x = 0;
this.y = 0;
}
this.x += 10;
this.y += 10;
};
we generally take it easy :)
// Rectangle - subclass
function Rectangle() { // Rectangle constructor
Shape.call(this); // call super constructor
}
Rectangle.prototype = Object.create(Shape.prototype); // inherit methods
Rectangle.prototype.moveAt = function(x, y) { // define new methods
this.x += x;
this.y += y;
console.info("Shape moved at: " + x + ", " + y);
};

var rect = new Rectangle(); // instantiate
rect instanceof Rectangle // true
rect.move(); // "Shape moved."
rect.moveAt(5, 2); // "Shape moved at: 5, 2"


Observers

let observer = {
observe: function(aSubject, aTopic, aData) {
if (aTopic == "some-topic") {
window.dump("Data received: " + aData);
}
}
};

// observer for a notification
Services.obs.addObserver(observer, "some-topic", false);

// stop observing
Services.obs.removeObserver(observer, "some-topic");

// somewhere, somebody does this:
observerService.notifyObservers(someObject, "some-topic", "some-data");


Lazy getters

XPCOMUtils.defineLazyGetter(myObject, "someProperty", function() {
// do some heavy duty stuff
// ...
return something;
});

// avoid disk activity, load modules only when needed
XPCOMUtils.defineLazyModuleGetter(this,
"FileUtils", "resource:///modules/FileUtils.jsm");


Debugger API + Scratchpad
(demo)

https://developer.mozilla.org/en-US/docs/Tools/Scratchpad
https://wiki.mozilla.org/Debugger
https://developer.mozilla.org/en-US/docs/JavaScript


Debugging JavaScript in Firefox
(demo)


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