letterCount.js

// Using the JavaScript language, have the function LetterCount(str) take the str parameter being passed and return the first word with the greatest number of repeated letters. For example: "Today, is the greatest day ever!" should return greatest because it has 2 e's (and 2 t's) and it comes before ever which also has 2 e's. If there are no words with repeating letters return -1. Words will be separated by spaces. 

// Input = "Hello apple pie"			Output = Hello
// Input = "No words"							Output = -1

function LetterCount( str ) {
	var words = str.split( ' ' );
	var longest = 0;
	var longest_word;
	for ( var i = 0; i < words.length; i++ ) {
		var word = words[i];
		for ( var j = 0; j < word.length; j++ ) {
			var pattern = new RegExp( word[j], 'gi' );
			var length = word.match( pattern ).length;
			if ( length > 1 && length > longest ) {
				longest = word.match( pattern ).length;
				longest_word = word;
			}
		}
	}
	
	return longest_word ? longest_word : -1;
}

Nice solution! One thing I'd watch out for is Unicode. This works well for ASCII text, but once you process languages with different scripts or combining characters, repeated-letter detection becomes a bit more challenging.