The Code:

<script language="javascript">
<!--
var X = new Array(          // just some sample data
		"l",
		"k",
		"j",
		"i",
		"h",
		"g",
		"f",
		"e",
		"d",
		"c",
		"b",
		"b"         // there's the duplicate
	);

function arrHasDupes( A ) {                          // finds any duplicate array elements using the fewest possible comparison
	var i, j, n;
	n=A.length;
                                                     // to ensure the fewest possible comparisons
	for (i=0; i<n; i++) {                        // outer loop uses each item i at 0 through n
		for (j=i+1; j<n; j++) {              // inner loop only compares items j at i+1 to n
			if (A[i]==A[j]) return true;
	}	}
	return false;
}

if ( arrHasDupes( X ) )                             // this just calls the function to test it
	document.write( "<H1>yes</H1>");
else
	document.write( "<H1>no</H1>");
-->
</script>