向下取整:var a = ~~1.2; //1

這個補充一下，還可以用位右移符>> var a = 3.4>>0; //3

但是兩者最好都只用在正整數上，因為只是舍掉了小數部分。Math.floor(-1.2)應該為-2，這兩種方法的結果為-1轉數字var time = + new Date();

設預設值function foo(bar){

var foobar = bar || "default";

//bar 為 undefined, null, "", 0, false, NaN 時最後都得到"default"

}

//坑

[]||"aa"; //[]

{}||"aa"; //SyntaxError

({})||"aa";//Object {}

NaN的坑//NaN - 不是一個數字

isNaN(a);

//檢查是不是 "不是一個數字" ..

isNaN(null);//false

//實際上是null被轉為0了,表面上"null 不是一個 不是數字 的東西"。wtf...

UNICODE 用作變數名var \u4f60\u597d = "\u4f60\u597d";

var b = {};

b.\u4f60\u597d = \u4f60\u597d;

console.log(b);//Object {你好: "你好"}

console.log(b.你好);// "你好"

console.log(b.\u4f60\u597d);// "你好"

console.log("你"==="\u4f60");//true

陣列傳遞和複製var a = [1,2,3];

var b = a;

delete b[1];

console.log(a);//[1, undefined × 1, 3]

var a = [4,5,6];

var b = a.slice(0);

delete b[1];

console.log(a);//[4,5,6]

console.log(b);//[4, undefined × 1,6]

物件與Functionconsole.log(typeof Function);//"function"

console.log(typeof Object);//"function"

函式宣告aa();

function aa(){return true;} //true

bb();

var bb = function(){return true;} //TypeError

toString()2.toString();//SyntaxError

2 .toString(); //"2"

2..toString(); //"2"

(2).toString(); //"2"

[1,[2,"abc","",0,null,undefined,false,NaN],3].toString();

//"1,2,abc,,0,,,false,NaN,3"

for in 暴露原型鏈屬性Object.prototype.foo = 1;

var obj = new Object();

obj.bar = 1;

for(var p in obj){

console.log(p);//bar,foo 都遍歷出來了。可以用hasOwnProperty()過濾原型鏈屬性

}

switch代替if else switch (true) {

case (a > 10):

do_something();

break;

case (a < 100):

others();

break;

default:

;

break;

};