1. ECMAScript 6 Harmony

2. Major Changes
• class, module
• ‘const’,‘let’, destructuring
• for of
• Iterator and generator
• Default parameter
• Rest parameter and spread
• Arrow function
• Map, Set,WeakMap
• Array comprehension
• Proxy
• String extra, quasi-string literal
• Binary, octet, unicode literal

3. class, module
• class, extends
• constructor
• super
• module
• import, export
import $ from “jQuery”;
module “point” {
export class PointT extends Time {
constructor(x, y, t) {
super(t);
public getX() { return x; }
public getY() { return y; }
}
toString() {
return '<' + this.getX() + ',' + this.getY() + '>';
}
}
}
import PointT from “point”;

4. ‘const’,‘let’, destructuring
• const
• let
• [x, y] = [y, x]
function Point5(x, y) {
const offset = 5;
if (x < offset) {
let y = 1;
x += y;
}
[x, y] = [ x+offset, y + offset];
return {x: x, y: y};
}

5. for of
• for (n of [ 1, 2, 3, 4, 5]) function Point6(x, y) {
var r = [1, 2, 3, 4, 5, 6, 7, 8, 9];
for (n of r) {
y = x + n;
}
return y;
}

6. Iterator and generator
• Iterator()
• #.next()
• yield
function Range(low, high) {
this.low = low;
this.high = high;
}
function RangeIterator(range) {
this.range = range;
this.current = this.range.low;
}
RangeIterator.prototype.next = function() {
if (this.current > this.range.high)
throw StopIteration;
else
return this.current++;
};
Range.prototype.__iterator__ = function() {
return new RangeIterator(this);
};
var range = new Range(3, 5);
for (var i in range) console.log(i);
function Range(low, high){
this.low = low;
this.high = high;
}
Range.prototype.__iterator__ = function(){
for (var i = this.low; i <= this.high; i++)
yield i;
};

7. Default parameter
• function (x=2) { } function Point7(x = 0, y = 0) {
return { x: x, y: y };
}
var p = Point7();

8. Rest parameter and spread
• function (...z) { }
• [1, 2, 3, ...[5, 6, 7]]
• f(...[2, 4, 6])
function f(w, x, y, z) {
return w * 1000 + x * 100 + y * 10 + z;
}
function g(...v) {
var w = v.length > 0 ? v[0] : 0;
var x = v.length > 1 ? v[1] : 0;
var y = v.length > 2 ? v[2] : 0;
var z = v.length > 3 ? v[3] : 0;
return w * 1000 + x * 100 + y * 10 + z;
}
var p = [2, 4, 6];
var q = [5, 7, ...p];
console.log(f(2,4,6,0));
console.log(g(2,4,6));
console.log(g(...q));

9. Arrow function
• function (a, b) { return a * b; }
• (a, b) => { a * b; }
• (a, b) => a * b;
• x => x * 3;
• () => {};
let empty = () => {};
let identity = x => x;
let square = x => x * x;
let key_maker = val => ({key: val});
let odds = evens.map(v => v + 1);
let fives = [];
nats.forEach(v => { if (v % 5 === 0) fives.push(v); });
const obj = {
method: function () {
return () => this;
}
};
assert(obj.method()() === obj);

10. Map, Set,WeakMap
• new Map()
• new Set()
• new WeakMap()
var m = new Map();
var s = new Set();
var w = new WeakMap();
var ko = {}, kf = function(){};
m.set(ko “object”);
m.set(kf,“function”);
m.set(“a”,“string”);
m.size == 3;
m.get(“a”);
m.get(ko);
m.get(kf);
s.set(5);
s.set(“string”);
s.size == 2;
s.has(5);
for (var n of s) console.log(n);

11. Array comprehension
• [n for (n of [5, 6, 7])] var a = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
var b = [n*2 for (n of a)];
var c = [n for (n of a) if (n % 2)];
var d = [i+j for (i of a) for (j of a)];

12. Proxy
• new Proxy({}, {}) var handler = {
get: function(target, name){
return name in target?
target[name] :
37;
}
};
var p = new Proxy({}, handler);
p.a = 1;
p.b = undefined;
console.log(p.a, p.b); // 1, undefined
console.log('c' in p, p.c); // false, 37

13. String extra, quasi-string literal
• startsWith
• endsWith
• contains
• toArray
• f`hello ${name}`
var s = “String extra, quasi-string literal”;
s.startsWith(“String”) == true;
s.endsWith(“literal”) == true;
s.contains(“quasi”) == true;
s.toArray();
function f(s) {
console.log(s);
return s;
}
var name = “everyone”;
f`hello ${name}.`;

14. Binary, octet, unicode literal
• 0b010101
• 0o77
• 'u{1d306}' == 'ud834udf06'