sentiment.js

function tokenize(input) {
  // convert negative contractions into negate_<word>
  return $.map(input.replace('.', '')
    .replace('/ {2,}/', ' ')
    .replace(/[.,\/#!$%\^&\*;:{}=_`~()]/g, '')
    .toLowerCase()
    .replace(/\w+['’]t\s+(a\s+)?(.*?)/g, 'negate_$2')
    .split(' '), $.trim);
}

function sentiment(phrase) {

  var tokens = tokenize(phrase),
    score = 0,
    words = [],
    positive = [],
    negative = [];

  // Iterate over tokens
  var len = tokens.length;
  while (len--) {
    var obj = tokens[len];
    var negate = obj.startsWith('negate_');

    if (negate) obj = obj.slice("negate_".length);

    if (!afinn.hasOwnProperty(obj)) continue;

    var item = afinn[obj];

    words.push(obj);
    if (negate) item = item * -1.0;
    if (item > 0) positive.push(obj);
    if (item < 0) negative.push(obj);

    score += item;
  }

  var verdict = score == 0 ? "NEUTRAL" : score < 0 ? "NEGATIVE" : "POSITIVE";

  var result = {
    verdict: verdict,
    score: score,
    comparative: score / tokens.length,
    positive: [...new Set(positive)],
    negative: [...new Set(negative)]
  };

  return result;
}