Here are 2 prototype-functions I created.

[HaganeNoKokoro]

Your way of figuring out the fraction is definitely better. I just pulled that other one out of my @$$, although it's aiming for the same "something/999" kind of thing.

Here's what I mean about marking up the string. I tell the function which part of the decimal repeats by putting it in square brackets

String.prototype.toRational=function() {
  var a=this.substring(0, this.indexOf("."));
  var b=this.substring(this.indexOf(".")+1, this.indexOf("["));
  var c=this.substring(this.indexOf("[")+1, this.indexOf("]"));
  
  var lena=a.length;
  var lenb=b.length;
  var lenc=c.length;

  var x=parseInt(a+b);
  var y=parseInt(a+b+c);
  
  var z=y-x;
  var den="";
  for(var i=0; i<lenc; i++) den+="9";
  for(var i=0; i<lenb; i++) den+="0";

  return z+"/"+den+"="+z/parseInt(den);
}
document.write("5.1[42857]".toRational());

[Ultimater]

A number of useful functions:

<script type="text/javascript">
Date.prototype.getShortDayOfWeek=function(){
return ["Sun","Mon","Tue","Wed","Thu","Fri","Sat"][this.getDay()]
}
Date.prototype.getShortMonth=function(){
return ["Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec"][this.getMonth()]
}
Date.prototype.toArmyTime=function(){
var hh=this.getHours();if(hh<10)hh="0"+hh;
var mm=this.getMinutes();if(mm<10)mm="0"+mm;
var ss=this.getSeconds();if(ss<10)ss="0"+ss;
return hh+":"+mm+":"+ss
}
Date.prototype.getDateFormat1=function(){
return this.getShortDayOfWeek()+" "+this.getShortMonth()+" "
+this.getDay()+" "+this.toArmyTime()+" "+this.getFullYear()
}

</script>
<script type="text/javascript">

var today = new Date(); 
alert(today.getDateFormat1())

</script>

[emblem]

<SCRIPT LANGUAGE="JavaScript" type="text/javascript">
String.prototype.splitAt=function(){return [this.substr(0,arguments[0]),this.substr(arguments[0])]}
</SCRIPT>

The above defines the prototype-function splitAt.

The following is an example of the function in use:

<SCRIPT LANGUAGE="JavaScript" type="text/javascript">
alert("abc".splitAt(2)[0])//alerts ab
alert("abc".splitAt(2)[1])//alerts c
</SCRIPT>

The way the function works:
The function always returns an Array with a length of 2 elements.
The given argument is the maxium string-length to allow for the the first element.
The second element is the remaining string that gets cut-off by the first element.

another way you can do this is:

String.prototype.splitAt=function(){return this.split(this.charAt(arguments[0]))}

[Ultimater]

Edit your post:
}

[emblem]

Edit your post:
}

nice call thanx

[Ultimater]

It doesn't replace my function for the same purpose.
Mind showing us how you intended to use yours?

[Ultimater]

Oh, I see how yours works now.
You are losing the character that you split at.
Also, yours is able to return more than two array-elements.

<SCRIPT LANGUAGE="JavaScript" type="text/javascript"> 
String.prototype.splitAt_Ultimater=function(){return [this.substr(0,arguments[0]),this.substr(arguments[0])]} 
String.prototype.splitAt_emblem=function(){return this.split(this.charAt(arguments[0]))}
</SCRIPT>
<SCRIPT LANGUAGE="JavaScript" type="text/javascript"> 
alert("abcabcabcabc".splitAt_Ultimater(3).length)
alert("abcabcabcabc".splitAt_emblem(3).length)
</SCRIPT>

[Ultimater]

It looks like when you made your splitAt function, you were thinging of the split function.
When I made my function, I was think about how to split a string into two parts and return the two w/o losing any part of the string.

[BigMoosie]

This does the same job as Math.abs(n) but is about 30% faster.

Number.prototype.abs=function(){return this>0?this:-this;}

[BigMoosie]

Array.toSource();

I needed to send a multi dimensional array to function through setTimeout, however this lost the internal structure of it so I created this that would turn it into a string that calling eval() would reconstruct it, and setTimeout is kind of like eval():

Array.prototype.toSource=function(){
	var L=this.length,s='[',t,i;
	for (i=0; i<L; i++) {
		if (i>0) s+=',';
		if (this[i].constructor==Array) s+=this[i].toSource();
		else switch (typeof this[i]) {
			case "number" : s+=this[i]; break;
			case "boolean" : s+=this[i]; break;
			default : s+='"'+this[i].toString().split('"').join('\\"')+'"';
		}
	}
	return s+']';
}

Obviously object references will be lost.

[BigMoosie]

If you dont mind losing the .toString() method of Arrays, you can use this, it does exactly the same as toSource() above ^ but is alot shorter.

Array.prototype.toString=function(){return '['+this.join(", ")+']';}

[A1ien51]

Here is one to grab a query string value. I am sure it could be done differently, but I was having fun with string manipulation and such.

<script type="text/javascript">

  String.prototype.GetQSValue = function(){
    if(!arguments[0])return null;
    var strFL = unescape(this)
    var regEx = new RegExp("[?&]" + arguments[0] + "=.*$","g");
    var strMatch = strFL.match(regEx);
    if(strMatch == null)return null
    var arrParts = strMatch.toString().split("&");
    return (arrParts[0].length==0)?arrParts[1].split("=")[1]:arrParts[0].split("=")[1];
  }

  var strLink = window.location.search;
  var strId = strLink.GetQSValue('id');
  alert(strId); 

</script>

Eric

[BigMoosie]

Array.prototype.binarySearch(term);

• Will return the index of a value in an array.
• If not found will return -1.
• Requires that the array be sorted before-hand.
• If there is more than one isntance it will not necasserily return the first one.
• Despite these drawbacks it is unbeleivably fast when using long arrays.

Array.prototype.binarySearch=function(q){
	var mid, lower=0, upper=this.length;
	while (lower<=upper) {
		mid=Math.floor((lower+upper)/2);
		if (q==this[mid]) return mid;
		if (q<this[mid]) upper=mid-1;
		else lower=mid+1
	}
	return -1;
}

[Scriptage]

String Encryption. I didn't write the algorithm or the source, I just adapted it into a prototype function.

[BigMoosie]

Is there a decyrption function to go with it?