javascript String sprintf

var sprintfWrapper={init:function(str,arg){var arguments=new Array();arguments[0]=str;for(var i in arg){arguments[1+parseInt(i)]=arg[i]}if(typeof arguments=="undefined"){return null}if(arguments.length<1){return null}if(typeof arguments[0]!="string"){return null}if(typeof RegExp=="undefined"){return null}var string=arguments[0];var exp=new RegExp(/(%([%]|(\-)?(\+|\x20)?(0)?(\d+)?(\.(\d)?)?([bcdfosxX])))/g);var matches=new Array();var strings=new Array();var convCount=0;var stringPosStart=0;var stringPosEnd=0;var matchPosEnd=0;var newString='';var match=null;while(match=exp.exec(string)){if(match[9]){convCount+=1}stringPosStart=matchPosEnd;stringPosEnd=exp.lastIndex-match[0].length;strings[strings.length]=string.substring(stringPosStart,stringPosEnd);matchPosEnd=exp.lastIndex;matches[matches.length]={match:match[0],left:match[3]?true:false,sign:match[4]||'',pad:match[5]||' ',min:match[6]||0,precision:match[8],code:match[9]||'%',negative:parseInt(arguments[convCount])<0?true:false,argument:String(arguments[convCount])}}strings[strings.length]=string.substring(matchPosEnd);if(matches.length==0){return string}if((arguments.length-1)<convCount){return null}var code=null;var match=null;var i=null;for(i=0;i<matches.length;i++){if(matches[i].code=='%'){substitution='%'}else if(matches[i].code=='b'){matches[i].argument=String(Math.abs(parseInt(matches[i].argument)).toString(2));substitution=sprintfWrapper.convert(matches[i],true)}else if(matches[i].code=='c'){matches[i].argument=String(String.fromCharCode(parseInt(Math.abs(parseInt(matches[i].argument)))));substitution=sprintfWrapper.convert(matches[i],true)}else if(matches[i].code=='d'){matches[i].argument=String(Math.abs(parseInt(matches[i].argument)));substitution=sprintfWrapper.convert(matches[i])}else if(matches[i].code=='f'){matches[i].argument=String(Math.abs(parseFloat(matches[i].argument)).toFixed(matches[i].precision?matches[i].precision:6));substitution=sprintfWrapper.convert(matches[i])}else if(matches[i].code=='o'){matches[i].argument=String(Math.abs(parseInt(matches[i].argument)).toString(8));substitution=sprintfWrapper.convert(matches[i])}else if(matches[i].code=='s'){matches[i].argument=matches[i].argument.substring(0,matches[i].precision?matches[i].precision:matches[i].argument.length);substitution=sprintfWrapper.convert(matches[i],true)}else if(matches[i].code=='x'){matches[i].argument=String(Math.abs(parseInt(matches[i].argument)).toString(16));substitution=sprintfWrapper.convert(matches[i])}else if(matches[i].code=='X'){matches[i].argument=String(Math.abs(parseInt(matches[i].argument)).toString(16));substitution=sprintfWrapper.convert(matches[i]).toUpperCase()}else{substitution=matches[i].match}newString+=strings[i];newString+=substitution}newString+=strings[i];return newString},convert:function(match,nosign){if(nosign){match.sign=''}else{match.sign=match.negative?'-':match.sign}var l=match.min-match.argument.length+1-match.sign.length;var pad=new Array(l<0?0:l).join(match.pad);if(!match.left){if(match.pad=="0"||nosign){return match.sign+pad+match.argument}else{return pad+match.sign+match.argument}}else{if(match.pad=="0"||nosign){return match.sign+match.argument+pad.replace(/0/g,' ')}else{return match.sign+match.argument+pad}}}}

String.prototype.sprintf = function(){
    return sprintfWrapper.init(this.toString(),arguments);
}
var s ="Thanks for the %s,num is %d,say %s";
console.log(s.sprintf('rose',21,'hi'));