JS cosine similarity - see also: http://www.p-value.info/2013/02/when-tfidf-and-cosine-similarity-fail.html

jscosine.js

function termFreqMap(str) {
	var words = str.split(' ');
	var termFreq = {};
	words.forEach(function(w) {
		termFreq[w] = (termFreq[w] || 0) + 1;
	});
	return termFreq;
}

function addKeysToDict(map, dict) {
	for (var key in map) {
		dict[key] = true;
	}
}

function termFreqMapToVector(map, dict) {
	var termFreqVector = [];
	for (var term in dict) {
		termFreqVector.push(map[term] || 0);
	}
	return termFreqVector;
}

function vecDotProduct(vecA, vecB) {
	var product = 0;
	for (var i = 0; i < vecA.length; i++) {
		product += vecA[i] * vecB[i];
	}
	return product;
}

function vecMagnitude(vec) {
	var sum = 0;
	for (var i = 0; i < vec.length; i++) {
		sum += vec[i] * vec[i];
	}
	return Math.sqrt(sum);
}

function cosineSimilarity(vecA, vecB) {
	return vecDotProduct(vecA, vecB) / (vecMagnitude(vecA) * vecMagnitude(vecB));
}

function textCosineSimilarity(strA, strB) {
	var termFreqA = termFreqMap(strA);
	var termFreqB = termFreqMap(strB);

	var dict = {};
	addKeysToDict(termFreqA, dict);
	addKeysToDict(termFreqB, dict);

	var termFreqVecA = termFreqMapToVector(termFreqA, dict);
	var termFreqVecB = termFreqMapToVector(termFreqB, dict);

	return cosineSimilarity(termFreqVecA, termFreqVecB);
}