Take a String and return the top N words found within the String, by frequency

top-words.js

(function top(string, num) {
    var words = string.toLowerCase().split(/[\s,.]+/),
    	count = {},
    	topWords = [];
    
    for(var i=0; i<words.length;i++){
        (count[words[i]] !== undefined) ? count[words[i]]++ : count[words[i]] = 1;
    }
    
    var list = Object.keys(count).sort(function(a, b){return count[a]-count[b];}).reverse();
    
    for(var i=0; i<num;i++) {
    	topWords.push(list[i]);
    }
    
    return topWords;
    
})('I scream, you scream, we all scream for ice cream',1)