javascript 点滴

indexOf(searchValue[, fromIndex]可以接受两个参数，第一个为要查询的值，第二个为参数是开始的索引搜索。
索引可以是负数，-1代表最后一个

    Array.isArray([]); //true      
    typeof  []   === "object" &&  Object.prototype.toString.call([]) === "[object Array]" 

 var a; a + 2    //NaN 
 var n = null; n + 3  //3

var unusualPropertyNames = {
  "": "An empty string",
  "!": "Bang!"
}
console.log(unusualPropertyNames."");   // SyntaxError: Unexpected string
console.log(unusualPropertyNames[""]);  // "An empty string"
console.log(unusualPropertyNames.!);    // SyntaxError: Unexpected token !
console.log(unusualPropertyNames["!"]); // "Bang!"

var foo = function bar() {
    bar();   //1
    foo();   //2
    arguments.callee(); //3
};

   var a5 = "Cat" && "Dog";    // t && t returns Dog
   var a6 = false && "Cat";    // f && t returns false
   var a7 = "Cat" && false;    // t && f returns false

 <a href = "javascript:void(document.forms[0].submit())">click me</a>  //提交

    var Xmas95 = new Date(1995, 11, 25)  //年 月 日 
    var Xmas95 = new Date(1995, 11, 25, 9, 30, 0); // 年月日 时分秒

function myFunc(theObject) {
  theObject.make = "Toyota";
}
var mycar = {make: "Honda", model: "Accord", year: 1998};
var x, y;
x = mycar.make; // "Honda"
myFunc(mycar);
y = mycar.make; // "Toyota"


function myFunc(theObject) {
  theObject = {make: "Ford", model: "Focus", year: 2006};
}
var mycar = {make: "Honda", model: "Accord", year: 1998};
var x, y;
x = mycar.make; // "Honda"
myFunc(mycar);
y = mycar.make; // "Honda"

    true 从服务器中加载页面，false从缓存中加载页面

12. 将数字转化为2，8，16进制形式的字符串

var num = 16;
num.toString(16) // "f"  

parseInt("AF",16) //以16进制转换：175 

function doAdd(){
	if(arguments.length ==1){
	console.log(arguments[0] + 10);
	} else if(arguments.length == 2){
	console.log(arguments[0] + arguments[1]);
	}
    }
doAdd(10);  //20
doAdd(30,20); //50

    window.onerror = function (sMessage, sUrl, sLine)//错误信息，哪个文件，行号
    try {
      window.nonExistentFunction();
      alert("Method completed.");
    } catch (exception) { alert("An exception occurred.");
    } finally { 
      alert("End of try卌atch test."); 
    }