Prototype Enumerable detect() Method

Syntax:

Iterator.detect([context]);

Return Value :

Returns first element for which the iterator returns true otherwise undefined.

Example:

<html>
<head>
<title>Prototype examples</title>
<script type="text/javascript" 
   src="/javascript/prototype.js">
</script>

<script>

function isPrime(n) {
  if (2 > n) return false;
  if (0 == n % 2) return (2 == n);
  for (var index = 3; n / index > index; index += 2)
    if (0 == n % index) return false;
  return true;
} // isPrime

function showResult(){
  alert($R(10,15).detect(isPrime) );
}

</script>
</head>

<body>

  <p>Click the button to see the result.</p>
  <br />
  <br />
  <input type="button" value="Result" onclick="showResult();"/>

</body>
</html>

To understand it in better way you can Try it yourself.