递归创建回调函数

var arr = [500,1000,3000,200] ;
var O = function(a,tt,s){
console.log(a)
if(tt){
//console.log(c)
setTimeout(function(){tt(s+1);},a)
};
}
var arrLength = arr.length;
var createCallbacki = function(i){
if(i <= arrLength){
O( arr[i+1] , function(){createCallbacki(i+1)},i )
}
}
var start = function(){
O( arr[0] , function(){createCallbacki(0)} ,0 )
}
start();