//ES6
for (let i = 0; i < a.length; i++) {
    let x = a[i];
    …
}
for (let i = 0; i < b.length; i++) {
    let y = b[i];
    …
}

let callbacks = [];
for (let i = 0; i <= 2; i++) {
    callbacks[i] = function () { 
        return i * 2; 
    };
}
callbacks[0]() === 0;
callbacks[1]() === 2;
callbacks[2]() === 4;

//ES5
var i, x, y;
for (i = 0; i < a.length; i++) {
    x = a[i];
    …
}
for (i = 0; i < b.length; i++) {
    y = b[i];
    …
}

var callbacks = [];
for (var i = 0; i <= 2; i++) {
    (function (i) {
        callbacks[i] = function() { 
            return i * 2; 
        };
    })(i);
}
callbacks[0]() === 0;
callbacks[1]() === 2;
callbacks[2]() === 4;

//ES6
{
    function foo () { return 1; }
    foo() === 1;
    {
        function foo () { return 2; }
        foo() === 2;
    }
    foo() === 1;
}

//ES5
//  only in ES5 with the help of block-scope emulating
//  function scopes and function expressions
(function () {
    var foo = function () { return 1; }
    foo() === 1;
    (function () {
        var foo = function () { return 2; }
        foo() === 2;
    })();
    foo() === 1;
})();

var foo = function(){
    return 'I am foo!';
}

var foo = () => {
    return 'I am foo!';
}

// ES6
odds  = evens.map(v => v + 1);
pairs = evens.map(v => ({ even: v, odd: v + 1 }));
nums  = evens.map((v, i) => v + i);

// ES5
odds  = evens.map(function (v) { return v + 1; });
pairs = evens.map(function (v) { return { even: v, odd: v + 1 }; });
nums  = evens.map(function (v, i) { return v + i; });

// ES6
nums.forEach(v => {
   if (v % 5 === 0)
       fives.push(v);
});

// ES5
nums.forEach(function (v) {
   if (v % 5 === 0)
       fives.push(v);
});

// ES6
this.nums.forEach((v) => {
    if (v % 5 === 0)
        this.fives.push(v);
});

// ES5

//  variant 1
var self = this;
this.nums.forEach(function (v) {
    if (v % 5 === 0)
        self.fives.push(v);
});

//  variant 2 (since ECMAScript 5.1 only)
this.nums.forEach(function (v) {
    if (v % 5 === 0)
        this.fives.push(v);
}.bind(this));

//  variant 3
this.nums.forEach(function (v) {
    if (v % 5 === 0)
        this.fives.push(v);
}, this);

//ES6
var customer = { name: "Foo" };
var card = { amount: 7, product: "Bar", unitprice: 42 };
var message = `Hello ${customer.name},
want to buy ${card.amount} ${card.product} for
a total of ${card.amount * card.unitprice} bucks?`;

//ES5
var customer = { name: "Foo" };
var card = { amount: 7, product: "Bar", unitprice: 42 };
var message = "Hello " + customer.name + ",\n" +
"want to buy " + card.amount + " " + card.product + " for\n" +
"a total of " + (card.amount * card.unitprice) + " bucks?";

//ES6
"hello".startsWith("ello", 1); // true
"hello".endsWith("hell", 4);   // true
"hello".includes("ell");       // true
"hello".includes("ell", 1);    // true
"hello".includes("ell", 2);    // false

//ES5
"hello".indexOf("ello") === 1;    // true
"hello".indexOf("hell") === (4 - "hell".length); // true
"hello".indexOf("ell") !== -1;    // true
"hello".indexOf("ell", 1) !== -1; // true
"hello".indexOf("ell", 2) !== -1; // false

//ES5
function msgAfterTimeout (msg, who, timeout, onDone) {
    setTimeout(function () {
        onDone(msg + " Hello " + who + "!");
    }, timeout);
}
msgAfterTimeout("", "Foo", 100, function (msg) {
    msgAfterTimeout(msg, "Bar", 200, function (msg) {
        console.log("done after 300ms:" + msg);
    });
});

//ES6
function msgAfterTimeout (msg, who, timeout) {
    return new Promise((resolve, reject) => {
        setTimeout(() => resolve(`${msg} Hello ${who}!`), timeout)
    })
}
msgAfterTimeout("", "Foo", 100).then((msg) =>
    msgAfterTimeout(msg, "Bar", 200)
).then((msg) => {
    console.log(`done after 300ms:${msg}`)
})

//ES6
var list = [ 1, 2, 3 ]
var [ a, , b ] = list
[ b, a ] = [ a, b ]

//ES5
var list = [ 1, 2, 3 ];
var a = list[0], b = list[2];
var tmp = a; a = b; b = tmp;

//ES6
var { op, lhs, rhs } = getASTNode()

//ES5
var tmp = getASTNode();
var op  = tmp.op;
var lhs = tmp.lhs;
var rhs = tmp.rhs;

//ES6
function f ([ name, val ]) {
    console.log(name, val)
}
function g ({ name: n, val: v }) {
    console.log(n, v)
}
function h ({ name, val }) {
    console.log(name, val)
}
f([ "bar", 42 ])
g({ name: "foo", val:  7 })
h({ name: "bar", val: 42 })

//ES5
function f (arg) {
    var name = arg[0];
    var val  = arg[1];
    console.log(name, val);
};
function g (arg) {
    var n = arg.name;
    var v = arg.val;
    console.log(n, v);
};
function h (arg) {
    var name = arg.name;
    var val  = arg.val;
    console.log(name, val);
};
f([ "bar", 42 ]);
g({ name: "foo", val:  7 });
h({ name: "bar", val: 42 });

//ES6
var list = [ 7, 42 ]
var [ a = 1, b = 2, c = 3, d ] = list
a === 7
b === 42
c === 3
d === undefined

//ES5
var list = [ 7, 42 ];
var a = typeof list[0] !== "undefined" ? list[0] : 1;
var b = typeof list[1] !== "undefined" ? list[1] : 2;
var c = typeof list[2] !== "undefined" ? list[2] : 3;
var d = typeof list[3] !== "undefined" ? list[3] : undefined;
a === 7;
b === 42;
c === 3;
d === undefined;

//ES6
function f (x, y = 7, z = 42) {
    return x + y + z
}
f(1) === 50

//ES5
function f (x, y, z) {
    if (y === undefined)
        y = 7;
    if (z === undefined)
        z = 42;
    return x + y + z;
};
f(1) === 50;

//ES6
function f (x, y, ...a) {
    return (x + y) * a.length
}
f(1, 2, "hello", true, 7) === 9

//ES5
function f (x, y) {
    var a = Array.prototype.slice.call(arguments, 2);
    return (x + y) * a.length;
};
f(1, 2, "hello", true, 7) === 9;

//ES6
var params = [ "hello", true, 7 ]
var other = [ 1, 2, ...params ] // [ 1, 2, "hello", true, 7 ]
f(1, 2, ...params) === 9

var str = "foo"
var chars = [ ...str ] // [ "f", "o", "o" ]

//ES5
var params = [ "hello", true, 7 ];
var other = [ 1, 2 ].concat(params); // [ 1, 2, "hello", true, 7 ]
f.apply(undefined, [ 1, 2 ].concat(params)) === 9;

var str = "foo";
var chars = str.split(""); // [ "f", "o", "o" ]

//ES6
class Shape {
    constructor (id, x, y) {
        this.id = id
        this.move(x, y)
    }
    move (x, y) {
        this.x = x
        this.y = y
    }
}

//ES5
var Shape = function (id, x, y) {
    this.id = id;
    this.move(x, y);
};
Shape.prototype.move = function (x, y) {
    this.x = x;
    this.y = y;
};

//ES6
class Rectangle extends Shape {
    constructor (id, x, y, width, height) {
        super(id, x, y)
        this.width  = width
        this.height = height
    }
}
class Circle extends Shape {
    constructor (id, x, y, radius) {
        super(id, x, y)
        this.radius = radius
    }
}

//ES5
var Rectangle = function (id, x, y, width, height) {
    Shape.call(this, id, x, y);
    this.width  = width;
    this.height = height;
};
Rectangle.prototype = Object.create(Shape.prototype);
Rectangle.prototype.constructor = Rectangle;
var Circle = function (id, x, y, radius) {
    Shape.call(this, id, x, y);
    this.radius = radius;
};
Circle.prototype = Object.create(Shape.prototype);
Circle.prototype.constructor = Circle;

//ES6
//  lib/math.js
export function sum (x, y) { return x + y }
export var pi = 3.141593

//  someApp.js
import * as math from "lib/math"
console.log("2π = " + math.sum(math.pi, math.pi))

//  otherApp.js
import { sum, pi } from "lib/math"
console.log("2π = " + sum(pi, pi))

//ES5
//  lib/math.js
LibMath = {};
LibMath.sum = function (x, y) { return x + y };
LibMath.pi = 3.141593;

//  someApp.js
var math = LibMath;
console.log("2π = " + math.sum(math.pi, math.pi));

//  otherApp.js
var sum = LibMath.sum, pi = LibMath.pi;
console.log("2π = " + sum(pi, pi));

//ES6
//  lib/mathplusplus.js
export * from "lib/math"
export var e = 2.71828182846
export default (x) => Math.exp(x)

//  someApp.js
import exp, { pi, e } from "lib/mathplusplus"
console.log("e^{π} = " + exp(pi))

//ES5
//  lib/mathplusplus.js
LibMathPP = {};
for (symbol in LibMath)
    if (LibMath.hasOwnProperty(symbol))
        LibMathPP[symbol] = LibMath[symbol];
LibMathPP.e = 2.71828182846;
LibMathPP.exp = function (x) { return Math.exp(x) };

//  someApp.js
var exp = LibMathPP.exp, pi = LibMathPP.pi, e = LibMathPP.e;
console.log("e^{π} = " + exp(pi));