Function factorial(num){
 if(num<=1){
 return 1;
 }else{
 return num*factorial(num-1);
 }
}

var anotherFactorial = factorial;
factorial = null;
alert(anotherFactorial)// 出错

function factorial (num){
 if(num){
 return 1;
 }else{
 return num*arguments.callee;
 }
}

var factorial = (function f(){
 if(num<1){
 return 1;
 }else{
 return num*f(num-1);
 }
})

//不建议传字符串,传递字符串可能导致性能损失 
setTimeout("alter('hello word')", 1000);
//推荐方式
setTimeout(function(){
 alter("Hello world");
},1000)
setInterval(function(){
 alter("Hello world");
},1000)

var num = 0, max = 0;
function incrrmentNumber{
 num++;
 if(num < max){
 setTimeout(incrrmentNumber,500);
 }else{
 alert("Done");
 }
}
setTimeout(incrrmentNumber,500);