wordfrequency.js

var words = (function(){

	var sWords = document.body.innerText.toLowerCase().trim().replace(/[,;.]/g,'').split(/[\s\/]+/g).sort();
	var iWordsCount = sWords.length; // count w/ duplicates

	// array of words to ignore
	var ignore = ['and','the','to','a','of','for','as','i','with','it','is','on','that','this','can','in','be','has','if'];
	ignore = (function(){
		var o = {}; // object prop checking > in array checking
		var iCount = ignore.length;
		for (var i=0;i<iCount;i++){
			o[ignore[i]] = true;
		}
		return o;
	}());

	var counts = {}; // object for math
	for (var i=0; i<iWordsCount; i++) {
		var sWord = sWords[i];
		if (!ignore[sWord]) {
			counts[sWord] = counts[sWord] || 0;
			counts[sWord]++;
		}
	}

	var arr = []; // an array of objects to return
	for (sWord in counts) {
		arr.push({
			text: sWord,
			frequency: counts[sWord]
		});
	}

	// sort array by descending frequency | http://stackoverflow.com/a/8837505
	return arr.sort(function(a,b){
		return (a.frequency > b.frequency) ? -1 : ((a.frequency < b.frequency) ? 1 : 0);
	});

}());

(function(){
	var iWordsCount = words.length; // count w/o duplicates
	for (var i=0; i<iWordsCount; i++) {
		var word = words[i];
		console.log(word.frequency, word.text);
	}
}());