typeof false // "boolean"
typeof .2 // "number"
typeof NaN // "number"
typeof '' // "string"
typeof undefined // "undefined"
typeof Symbol() // "symbol"
typeof new Date() // "object"
typeof [] // "object"
typeof alert // "function"
typeof null // "object"
typeof not_defined_var // "undefined"

var global_var = 1;
function fn () {
var fn_var = 2;
if(fn_var > 10){
let block_var = 3;
global_var2 = 4;
}
}

const num = 1;
const obj = {
prop: 'value'
};
num = 2; // Uncaught TypeError: Assignment to constant variable.
obj['prop'] = 'value2';
obj = []; // Uncaught TypeError: Assignment to constant variable.

console.log(a); // undefined
var a = 2;

var a;
console.log(a);
a = 2;

function fn(){}
var fn = function(){}
var fn = new Function(arg1, arg2, ... argN, funcBody)
var fn = (param) => {}

function foo() {
return arguments;
}
foo(1, 2, 3); // Arguments[3] 
// { "0": 1, "1": 2, "2": 3 } 

function foo(...args) {
return args;
}
foo(1, 2, 3); // Array[3]
// [1, 2, 3]
function fn(a, b, ...args){
return args;
}
fn(1, 2, 3, 4, 5); // Array[3] 
// [3, 4, 5] 

function fn (a = 2, b = 3) {
return a + b;
}
fn(2, 3); // 5
fn(2); // 5
fn(); // 5

var obj = {
prop: 'value',
fn: function(){}
};
var date = new Date();

function People(name, age) {
this.name = name;
this.age = age;
}
var people = new People('Byron', 26);

function Person(name) {
this.name = name;
}
Person.prototype.print = function () {
console.log(this.name);
};
var p1 = new Person('Byron');
var p2 = new Person('Casper');
p1.print();
p2.print();

function isNumber(obj) {
return Object.prototype.toString.call(obj) === '[object Number]';
} 

function fn() {
this.i = 0;
setInterval(function () {
console.log(this.i++);
}.bind(this), 500)
}
fn(); 
() => {}

function fn() {
this.i = 0;
setInterval(() => {
console.log(this.i++);
}, 500)
}
fn();

function inherits(child, parent) {
var _proptotype = Object.create(parent.prototype);
_proptotype.constructor = child.prototype.constructor;
child.prototype = _proptotype;
}
function People(name, age) {
this.name = name;
this.age = age;
}
People.prototype.getName = function () {
return this.name;
}
function English(name, age, language) {
People.call(this, name, age);
this.language = language;
}
inherits(English, People);
English.prototype.introduce = function () {
console.log('Hi, I am ' + this.getName());
console.log('I speak ' + this.language);
}
function Chinese(name, age, language) {
People.call(this, name, age);
this.language = language;
}
inherits(Chinese, People);
Chinese.prototype.introduce = function () {
console.log('你好，我是' + this.getName());
console.log('我说' + this.language);
}
var en = new English('Byron', 26, 'English');
var cn = new Chinese('色拉油', 27, '汉语');
en.introduce();
cn.introduce();

"use strict";
class People{
constructor(name, age){
this.name = name;
this.age = age;
}
getName(){
return this.name;
}
}
class English extends People{
constructor(name, age, language){
super(name, age);
this.language = language;
}
introduce(){
console.log('Hi, I am ' + this.getName());
console.log('I speak ' + this.language);
}
}
let en = new English('Byron', 26, 'English');
en.introduce();

for (var i = 0; i < 10; i++) {
for (var j = 0; j < 5; j++) {
console.log(j);
if (j === 1) {
break loop;
}
}
}
console.log(i);

var x = { a:1 };
{ a:1 }
{ a:1, b:2 }

( function() {}() );
( function() {} )();
[ function() {}() ];
~ function() {}();
! function() {}();
+ function() {}();
- function() {}();
delete function() {}();
typeof function() {}();
void function() {}();
new function() {}();
new function() {};
var f = function() {}();
1, function() {}();
1 ^ function() {}();
1 > function() {}();

[1, 2, 3, 4].forEach(function(item){
console.log(item);
});

function makeCounter(init) {
var init = init || 0;
return function(){
return ++init;
}
}
var counter = makeCounter(10);
console.log(counter());
console.log(counter());

for (var i = 0; i < doms.length; i++) {
doms.eq(i).on('click', function (ev) {
console.log(i);
});
} 
for (var i = 0; i < doms.length; i++) {
(function (i) {
doms.eq(i).on('click', function (ev) {
console.log(i);
});
})(i);
}

function eventBinderGenerator() {
if (window.addEventListener) {
return function (element, type, handler) {
element.addEventListener(type, hanlder, false);
}
} else {
return function (element, type, handler) {
element.attachEvent('on' + type, handler.bind(element, window.event));
}
}
}
var addEvent = eventBinderGenerator();

function isType(type) {
return function(obj){
return Object.prototype.toString.call(obj) === '[object '+ type +']';
}
}
var isNumber = isType('Number');
console.log(isNumber(1));
console.log(isNumber('s'));
var isArray = isType('Array');
console.log(isArray(1));
console.log(isArray([1, 2, 3])); 
function f(n) {
return n * n;
}
function g(n) {
return n * 2;
}
console.log(f(g(5)));
function pipe(f, g) {
return function () {
return f.call(null, g.apply(null, arguments));
}
}
var fn = pipe(f, g);
console.log(fn(5));

function factorial(n) {
if (n === 1) return 1;
return n * factorial(n - 1);
}
factorial(5) // 120

function factorial(n, total) {
if (n === 1) return total;
return factorial(n - 1, n * total);
}
factorial(5, 1) // 120

function currying(fn, n) {
return function (m) {
return fn.call(this, m, n);
};
}
function tailFactorial(n, total) {
if (n === 1) return total;
return tailFactorial(n - 1, n * total);
}
const factorial = currying(tailFactorial, 1);
factorial(5) // 120

Function.prototype.uncurry = function () {
return this.call.bind(this);
};

var push = Array.prototype.push.uncurry();
var arr = [];
push(arr, 1);
push(arr, 2);
push(arr, 3);
console.log(arr);