This document discusses the misunderstandings around JavaScript and provides examples of how compilation and scoping work in JavaScript. It shows how functions are compiled without type or overflow checks and how typed arrays can be used. It also demonstrates class inheritance, constructors, closures, block scoping with let, and the current state of ES6 compatibility. The overall message is that any application that can be written in JavaScript will likely be written in JavaScript.

2. Javascript sucks
2014 perspective

3. JavaScript:
The World's
Most
Misunderstood
Programming
Language

19. One Step Back:
How Compilation Works

20. infer types
function compiledCalculation() {
var x = f()|0; // x is a 32-bit value
var y = g()|0; // so is y
return (x+y)|0; // 32-bit addition, no type or overflow
checks
}

21. typed arrays
var MEM8 = new Uint8Array(1024*1024);
var MEM32 = new Uint32Array(MEM8.buffer); // alias
MEM8's data function
compiledMemoryAccess(x) {
MEM8[x] = MEM8[x+10]; // read from x+10, write to x
MEM32[(x+16)>>2] = 100;
}

22. Strlen example
function strlen(ptr) { // calculate length of C
string ptr = ptr|0;
var curr = 0;
curr = ptr;
while (MEM8[curr]|0 != 0) {
curr = (curr + 1)|0;
}
return (curr - ptr)|0;
}

23.  http://kripken.github.io/boon/boon.html

26. class RaceCar extends Car { //inheritance
constructor(make, topSpeed) {
super(make); //call the parent constructor with super
this.topSpeed = topSpeed;
}
goFast(){
this.currentSpeed = this.topSpeed;
}

27. class Car {
constructor(make) { //constructors!
this.make = make;
this.currentSpeed = 25;
}
printCurrentSpeed(){
console.log(this.make + ' is going ' + this.currentSpeed
+ ' mph.');
}
}

28. let stang = new RaceCar('Mustang', 150);
stang.printCurrentSpeed();
stang.goFast();
stang.printCurrentSpeed();

30. function Car() {
var self = this; //locally assign this that can be closed over
self.speed = 0;
setInterval(function goFaster() {
//this has a different scope, but we can use the self variable to
reference the parent "this"
self.speed += 5;
console.log('now going: ' + self.speed);
}, 1000);
}
var car = new Car();

31. function Car() { //Note, we could use the new Class feature
in ES6 instead
this.speed = 0;
setInterval(() => {
this.speed += 5; //this is from Car
console.log
console.log('now going: ' + this.speed);
}, 1000);
}

33. <module>
import $ from 'lib/jquery';
var x = 123;
// The current scope is not global
console.log('$' in window); // false
console.log('x' in window); // false
// `this` still refers to the global object
console.log(this === window); // true
</module>

35. var num = 0; //globally scoped
for (let i = 0; i < 10; i++) { //i is block scoped
num += i;
console.log('value of i in block: ' + i);
}
console.log('value of i out of block: ' + i);

37. Where are we now?
 https://kangax.github.io/compat-table/es6/

38. Any application that can be
written in JavaScript, will
eventually be written in
JavaScript.
2014 perspective

39. Thank you