This document summarizes the major changes in ECMAScript 6 (ES6), also known as ECMAScript 2015. Some key changes include the introduction of classes, modules, iterators, generators, default parameters, rest parameters, arrow functions, new data structures like Map and Set, string padding capabilities, template literals, and new numeric literal syntaxes for binary, octal and Unicode characters. ES6 aims to make JavaScript code more modular and reusable through these new features.

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'