let a = 100;
typeof a;//number
a = undefined;
typeof a;//undefined
a = null;
typeof a;//null

5 == true;//false。true会先转换为1，false转换为0
'12' + 1;//'123'。数字先转换成字串
'12' - 1;//11。字串先转换成数字
[] == false;//true。数组转换为其他类型时，取决于另一个比较者的类型
[] == 0;//true
[2] == '2';//true
[2] == 2;//true
[] - 2;//-2
12 + {a:1};//"12[object Object]"。这里对象先被转换成了字串
null == false;//false
null == 0;//false
null - 1;//-1

let str = '23abGdH4d4Kd';
str = str.replace(/([a-z]*)([A-Z]*)/g, function(match, $1 , $2){return $1.toUpperCase() + $2.toLowerCase()});//"23ABgDh4D4kD"

str = 'web-application-development';
str = str.replace(/-([a-z])/g, (replace)=>replace[1].toUpperCase());//"webApplicationDevelopment"(驼峰转换)

str = Math.random().toString(36).substring(2) 

//方法一：通过中间数组完成交换
let a = 1,
 b = 2;
a = [b, b = a][0];

//方法二：通过加减运算完成交换
let a = 1,
 b = 2;
a = a + b;
b = a - b;
a = a - b;

//方法三：通过加减运算完成交换
let a = 1,
 b = 2;
a = a - b;
b = a + b;
a = b - a;

//方法四：通过两次异或还原完成交换。另外，这里不会产生溢出
let a = 1,
 b = 2;
a = a ^ b;
b = a ^ b;
a = a ^ b;
//方法五：通过乘法运算完成交换
let a = 1,
 b = 2;
a = b + (b = a) * 0; 

. 4.53 / 2 = 2.265
. 4.53 % 2 = 0.5300000000000002
. 5 % 3 = 2

function ClassA(sColor) {
 this.color = sColor;
}

ClassA.prototype.sayColor = function () {
 alert(this.color);
};

function ClassB(sColor, sName) {
 ClassA.call(this, sColor);
 this.name = sName;
}

ClassB.prototype = new ClassA();

ClassB.prototype.sayName = function () {
 alert(this.name);
};

var objA = new ClassA("blue");
var objB = new ClassB("red", "John");
objA.sayColor(); //输出 "blue"
objB.sayColor(); //输出 "red"
objB.sayName(); //输出 "John"

function list() {
 return Array.prototype.slice.call(arguments);
}

var list1 = list(1, 2, 3); // [1, 2, 3]

// Create a function with a preset leading argument
var leadingThirtysevenList = list.bind(undefined, 37);

var list2 = leadingThirtysevenList(); // [37]
var list3 = leadingThirtysevenList(1, 2, 3); // [37, 1, 2, 3]

function memoizer(fundamental, cache) { 
 let cache = cache || {}, 
 shell = function(arg) { 
 if (! (arg in cache)) { 
 cache[arg] = fundamental(shell, arg); 
 } 
 return cache[arg]; 
 }; 
 return shell; 
} 
 

let singleton = function(){
 let obj;
 return function(){
 return obj || (obj = new Object());
 }
}();

let variables = {
 key1: 'value1',
 key2: 'value2'
},
 fnBody = 'return this.key1 + ":" + this.key2',
 fn = new Function(fnBody);
console.log(fn.apply(variables));

let ul = document.getElementsByTagName("ul")[0],
 docfrag = document.createDocumentFragment();

const browserList = [
 "Internet Explorer", 
 "Mozilla Firefox", 
 "Safari", 
 "Chrome", 
 "Opera"
];

browserList.forEach((e) => {
 let li = document.createElement("li");
 li.textContent = e;
 docfrag.appendChild(li);
});

ul.appendChild(docfrag);

function Fibonacci (n) {
 if ( n <= 1 ) {return 1};
 return Fibonacci(n - 1) + Fibonacci(n - 2);
}
Fibonacci(10); // 89
Fibonacci(50);// 20365011074，耗时10分钟左右才能出结果
Fibonacci(100);// 这里就一直出不了结果，也没有错误提示

function Fibonacci2 (n , ac1 = 1 , ac2 = 1) {
 if( n <= 1 ) {return ac2};
 return Fibonacci2 (n - 1, ac2, ac1 + ac2);
}
Fibonacci2(100) // 573147844013817200000
Fibonacci2(1000) // 7.0330367711422765e+208
Fibonacci2(10000) // Infinity. "Uncaught RangeError:Maximum call stack size exceeded"

function trampoline(f) {
 while (f && f instanceof Function) {
 f = f();
 }
 return f;
}

//改造Fibonacci2()的定义
function Fibonacci2 (n , ac1 = 1 , ac2 = 1) {
 if( n <= 1 ) {return ac2};
 return Fibonacci2.bind(undefined, n - 1, ac2, ac1 + ac2);
}
trampoline(Fibonacci2(100));//573147844013817200000