StevenJL

// Without arrow functions
class MyComponent extends React.Component {  
 
  /* 
    We define a method on MyComponent objects, that
    requires access to the MyComponent object as `this`.
  */
  updateFoo() {
    this.setState({
      foo: "bar"

StevenJL

// lib/math.js
export function sum(x, y) { return x + y; }
export var pi = 3.14159

// myApp.js
import {sum, pi} from "lib/math"
sum(pi, pi);

// otherApp.js
import * as math from "lib/math"

StevenJL

// Array Matching
var list = [1, 2, 3]
var [a, , b] = list
a // => 1
b // => 3
[b, a] = [a, b]
a // => 3
b // => 1

// Object Matching

StevenJL

// Before ES6
function Person(name, age) {
  this.name = name;
  this.age = age;
}

// a greeter method on a Person object
Person.prototype.greet = function() {
  console.log('Hi, I am ' + this.name);
}

StevenJL

// create a monkey constructor
function Monkey(favorite_food) {
  this.favorite_food = favorite_food;
}

// set a method on the monkey constructor
Monkey.prototype.wait_and_ask = function() {
  setTimeout(function () {
    console.log('It has been 2 seconds, may I have a ' + this.favorite_food);
  }, 2000);

StevenJL

// before ES6
var numbers = [1,2,3,4,5,6];
var even_numbers = numbers.filter(function(x) { return x%2 === 0 })

// with ES6
const numbers = [1,2,3,4,5,6];
const even_numbers = numbers.filter(x => x%2 === 0 })

StevenJL

// cannot re-assign a const variable
const x = "written in stone";
x = "changed my mind"; // raises TypeError: Assignment to constant variable

// but you can still mutate a const variable
const person = {};
person.name = "Steve";

/*
`const` is great for assigning to a module that is required into code, 

StevenJL

if (false) {
  var x = "never_assigned";
}
x //=> returns undefined instead of raising error

if (false) {
  let x = "never_assigned";
}
x //=> raises a ReferenceError: x not defined

StevenJL

/*
  GLOBAL SCOPE
*/
var global_var = "mango"; // global_var is accessible everywhwere

/*
  Function scope is lexical
*/
function otherFunction() {
  var outer_var = "foo";

StevenJL

// You can create a string as a character array
char some_text[] = "Here is some text";

// However, you cannot first instantiate a character array
// and then assign to a string.
char some_text[20];
some_text = "Here is some text";  // WRONG

// If you want to instantiate a variable first, and then
// assign to a string, you must use a pointer