[10] == 10 // true
[10] === 10 // false
"10" == 10 // true
"10" === 10 // false
[] == 0 // true
[] === 0 // false
"" == false // true 但是 true == "a" 是false
"" === false // false 

var one = '1';
var numberOne = +one; // Number 1 

var one = '1';
var negativeNumberOne = -one; // Number -1 

var list = [1, 2, 3, 4];
function empty() {
//清空数组
list = [];
}
empty(); 

var list = [1, 2, 3, 4];
function empty() {
//清空数组
list.length = 0;
}
empty(); 

var foo = [1,2,3];
var bar = [1,2,3];
var foo2 = foo;
var bar2 = bar;
foo = [];
bar.length = 0;
console.log(foo, bar, foo2, bar2);
//[] [] [1, 2, 3] [] 

function shuffle(arr) {
var i,
j,
temp;
for (i = arr.length - 1; i > 0; i--) {
j = Math.floor(Math.random() * (i + 1));
temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;
}
return arr; 
}; 

var a = [1, 2, 3, 4, 5, 6, 7, 8];
var b = shuffle(a);
console.log(b);
// [2, 7, 8, 6, 5, 3, 1, 4] 

function Person(name) {
this.name = name;
this.sayName = function() {
console.log("Hello my name is: ", this.name);
return this;
};
this.changeName = function(name) {
this.name = name;
return this;
};
}
var person = new Person("John");
person.sayName().changeName("Timmy").sayName();
//Hello my name is: John
//Hello my name is: Timmy 

var one = 1;
var two = 2;
var three = '3';
var result = ''.concat(one, two, three); //"123" 

var one = 1;
var two = 2;
var three = '3';
var result = one + two + three; //"33" 而不是 "123" 

// 单位移
console.log(~1337) // -1338
// 双位移
console.log(~~47.11) // -> 47
console.log(~~-12.88) // -> -12
console.log(~~1.9999) // -> 1
console.log(~~3) // -> 3
//失败的情况
console.log(~~[]) // -> 0 
console.log(~~NaN) // -> 0
console.log(~~null) // -> 0
//大于32位整数则失败
console.log(~~(2147483647 + 1) === (2147483647 + 1)) // -> 0 

if (!module.parent) {
// 运行 `node something.js`
app.listen(8088, function() {
console.log('app listening on port 8088');
})
} else {
// 使用 `require('/.something.js')`
module.exports = app;
}

function callback() {
console.log('Hi human');
}
document.getElementById('someelem').addEventListener('click', callback); 

function callback(a, b) {
return function() {
console.log('sum = ', (a+b));
}
}
var x = 1, y = 2;
document.getElementById('someelem').addEventListener('click', callback(x, y)); 

var alertText = function(text) {
alert(text);
};
document.getElementById('someelem').addEventListener('click', alertText.bind(this, 'hello')); 

var someText = 'JavaScript rules';
if (someText.indexOf('JavaScript') !== -1) {
}
// 或者
if (someText.indexOf('JavaScript') >= 0) {
} 

// examples/mvc/lib/boot.js
for (var key in obj) {
// "reserved" exports
if (~['name', 'prefix', 'engine', 'before'].indexOf(key)) continue;

// examples/lib/utils.js
exports.normalizeType = function(type){
return ~type.indexOf('/')
? acceptParams(type)
: { value: mime.lookup(type), params: {} };
};

// examples/web-service/index.js
// key is invalid
if (!~apiKeys.indexOf(key)) return next(error(401, 'invalid api key')); 

var someText = 'text';
!!~someText.indexOf('tex'); // someText 包含 "tex" - true
!~someText.indexOf('tex'); // someText 不包含 "tex" - false
~someText.indexOf('asd'); // someText 不包含 "asd" - false
~someText.indexOf('ext'); // someText 包含 "ext" - true
String.prototype.includes() 

// arrow函数的日常语法
param => expression
// 可能也会写在括号中
// 括号是多参数要求
(param1 [, param2]) => expression

// 使用日常函数
var arr = [5,3,2,9,1];
var arrFunc = arr.map(function(x) {
return x * x;
});
console.log(arr)

// 使用arrow函数
var arr = [5,3,2,9,1];
var arrFunc = arr.map((x) => x*x);
console.log(arr) 

// 全局定义this.i
this.i = 100;
var counterA = new CounterA();
var counterB = new CounterB();
var counterC = new CounterC();
var counterD = new CounterD();

// 不好的示例
function CounterA() {
// CounterA's `this` 实例 (!! 忽略这里)
this.i = 0;
setInterval(function () {
// `this` 指全局对象，而不是 CounterA's `this`
// 因此，开始计数与100，而不是0 (本地的 this.i)
this.i++;
document.getElementById("counterA").innerHTML = this.i;
}, 500);
}
// 手动绑定 that = this
function CounterB() {
this.i = 0;
var that = this;
setInterval(function() {
that.i++;
document.getElementById("counterB").innerHTML = that.i;
}, 500);
}
// 使用 .bind(this)
function CounterC() {
this.i = 0;
setInterval(function() {
this.i++;
document.getElementById("counterC").innerHTML = this.i;
}.bind(this), 500);
}
// 使用 arrow函数
function CounterD() {
this.i = 0;
setInterval(() => {
this.i++;
document.getElementById("counterD").innerHTML = this.i;
}, 500);
}

console.time("Array initialize");
var arr = new Array(100),
len = arr.length,
i;
for (i = 0; i < len; i++) {
arr[i] = new Object();
};
console.timeEnd("Array initialize"); // 输出: Array initialize: 0.711ms 

const _err = function( message ){
throw new Error( message );
}
const getSum = (a = _err('a is not defined'), b = _err('b is not defined')) => a + b
getSum( 10 ) // throws Error, b is not defined
getSum( undefined, 10 ) // throws Error, a is not defined 

function doTheThing() {
// 错误: notDeclared is not defined
console.log(notDeclared);
// 输出: undefined
console.log(definedLater);
var definedLater;
definedLater = 'I am defined!'
// 输出: 'I am defined!'
console.log(definedLater)
// Outputs: undefined
console.log(definedSimulateneously);
var definedSimulateneously = 'I am defined!'
// 输出: 'I am defined!'
console.log(definedSimulateneously)
// 输出: 'I did it!'
doSomethingElse();
function doSomethingElse(){
console.log('I did it!');
}
// 错误: undefined is not a function
functionVar();
var functionVar = function(){
console.log('I did it!');
}
}

var myObject = {
name: '@tips_js'
};
if (myObject.name) { ... } 

var myObject = {
name: '@tips_js'
};
myObject.hasOwnProperty('name'); // true
'name' in myObject; // true
myObject.hasOwnProperty('valueOf'); // false, valueOf 是从原型链继承的
'valueOf' in myObject; // true 

var myFunc = function() {
this.name = '@tips_js';
};
myFunc.prototype.age = '10 days';
var user = new myFunc();
user.hasOwnProperty('name'); // true
user.hasOwnProperty('age'); // false, 因为age是原型链上的 

var firstName = 'Jake';
var lastName = 'Rawr';
console.log('My name is ' + firstName + ' ' + lastName);
// My name is Jake Rawr 
模板字符串：
var firstName = 'Jake';
var lastName = 'Rawr';
console.log(`My name is ${firstName} ${lastName}`);
// My name is Jake Rawr 

const nodelist = document.querySelectorAll('div');
const nodelistToArray = Array.apply(null, nodelist);
//later on ..
nodelistToArray.forEach(...);
nodelistToArray.map(...);
nodelistToArray.slice(...);
//etc... 

const nodelist = [...document.querySelectorAll('div')]; // 返回的是个真实的数组
//later on ..
nodelist.forEach(...);
nodelist.map(...);
nodelist.slice(...);
//etc... 

// 整个script文件都将是严格模式语法
"use strict";
var v = "Hi! I'm a strict mode script!";
或者在函数内：
function f()
{
// 函数范围内的严格模式语法
'use strict';
function nested() { return "And so am I!"; }
return "Hi! I'm a strict mode function! " + nested();
}
function f2() { return "I'm not strict."; }

function printUpperCase(words) {
var elements = [].concat(words);
for (var i = 0; i < elements.length; i++) {
console.log(elements[i].toUpperCase());
}
}

printUpperCase("cactus");
// => CACTUS
printUpperCase(["cactus", "bear", "potato"]);
// => CACTUS
// BEAR
// POTATO 

['Shanghai', 'New York', 'Mumbai', 'Buenos Aires'].sort();
// ["Buenos Aires", "Mumbai", "New York", "Shanghai"] 

// Spanish
['único','árbol', 'cosas', 'fútbol'].sort();
// ["cosas", "fútbol", "árbol", "único"] // 错误的排序
// German
['Woche', 'wöchentlich', 'wäre', 'Wann'].sort();
// ["Wann", "Woche", "wäre", "wöchentlich"] // 错误的排序 

['único','árbol', 'cosas', 'fútbol'].sort(function (a, b) {
return a.localeCompare(b);
});
// ["árbol", "cosas", "fútbol", "único"]
['Woche', 'wöchentlich', 'wäre', 'Wann'].sort(function (a, b) {
return a.localeCompare(b);
});
// ["Wann", "wäre", "Woche", "wöchentlich"] 

['único','árbol', 'cosas', 'fútbol'].sort(Intl.Collator().compare);
// ["árbol", "cosas", "fútbol", "único"]
['Woche', 'wöchentlich', 'wäre', 'Wann'].sort(Intl.Collator().compare);
// ["Wann", "wäre", "Woche", "wöchentlich"] 

if (color) {
if (color === 'black') {
printBlackBackground();
} else if (color === 'red') {
printRedBackground();
} else if (color === 'blue') {
printBlueBackground();
} else if (color === 'green') {
printGreenBackground();
} else {
printYellowBackground();
}
}

switch(color) {
case 'black':
printBlackBackground();
break;
case 'red':
printRedBackground();
break;
case 'blue':
printBlueBackground();
break;
case 'green':
printGreenBackground();
break;
default:
printYellowBackground();
}

switch(true) {
case (typeof color === 'string' && color === 'black'):
printBlackBackground();
break;
case (typeof color === 'string' && color === 'red'):
printRedBackground();
break;
case (typeof color === 'string' && color === 'blue'):
printBlueBackground();
break;
case (typeof color === 'string' && color === 'green'):
printGreenBackground();
break;
case (typeof color === 'string' && color === 'yellow'):
printYellowBackground();
break;
}

var colorObj = {
'black': printBlackBackground,
'red': printRedBackground,
'blue': printBlueBackground,
'green': printGreenBackground,
'yellow': printYellowBackground
};

if (color in colorObj) {
colorObj[color]();
}

//不好的
...
render() {
<div key={{item.key}}>{{item.name}}</div>
}
...
//好的
<MyComponent key={{item.key}}/> 
· 使用数组不是个好习惯
· random()从不会执行
//不好的
<MyComponent key={{Math.random()}}/> 

$scope.$apply(() => {
$scope.tip = 'Javascript Tip';
}); 

var arr = [1,2,3,4,5];
arr.push(6);
arr[arr.length] = 6; //在Chrome 47.0.2526.106 (Mac OS X 10.11.1)上提高了 43% 的速度 

var arr = [1,2,3,4,5];
arr.unshift(0);
[0].concat(arr); //在Chrome 47.0.2526.106 (Mac OS X 10.11.1)上提高了 98% 的速度 

var items = ['one', 'two', 'three', 'four'];
items.splice(items.length / 2, 0, 'hello');