diff --git a/.eslintrc b/.eslintrc
index 4739f5f..6144af8 100644
--- a/.eslintrc
+++ b/.eslintrc
@@ -12,5 +12,8 @@
     "env": {
         "node": true
     },
+    "parserOptions": {
+        "ecmaVersion": 8
+    },
     "extends": "eslint:recommended"
 }
diff --git a/build/build.js b/build/build.js
index 806fb10..23cb764 100644
--- a/build/build.js
+++ b/build/build.js
@@ -1,79 +1,66 @@
-var async = require('async');
-var fs = require('fs');
-var path = require('path');
+const fs = require('fs');
+const path = require('path');
 
 // File paths
-var EMOJI_PATH = path.resolve(__dirname, 'Emoji_Sentiment_Data_v1.0.csv');
-var RESULT_PATH = path.resolve(__dirname, 'emoji.json');
+const EMOJI_PATH = path.resolve(__dirname, 'Emoji_Sentiment_Data_v1.0.csv');
+const RESULT_PATH = path.resolve(__dirname, 'emoji.json');
 
 /**
- * Read emoji data from original format (CSV).
- * @param  {object}   hash     Result hash
- * @param  {Function} callback Callback
- * @return {void}
+ * Reads emoji data from original format (CSV).
+ * @param  {object}   hash     Result hash.
+ * @return {object}   hash     Result hash.
  */
-function processEmoji(hash, callback) {
+const processEmoji = async () => {
+    let hash = {};
     // Read file
-    fs.readFile(EMOJI_PATH, 'utf8', function (err, data) {
-        if (err) return callback(err);
-
-        // Split data by new line
-        data = data.split(/\n/);
-
-        // Iterate over dataset and add to hash
-        for (var i in data) {
-            var line = data[i].split(',');
-
-            // Validate line
-            if (i == 0) continue;               // Label
-            if (line.length !== 9) continue;    // Invalid
+    const data = await fs.readFileSync(EMOJI_PATH, 'utf8');
+    // Split data by new line
+    const lines = data.split(/\n/);
+    // Iterate over dataset and add to hash
+    for (const i in lines) {
+        const line = lines[i].split(',');
+        // Validate line
+        if (i === '0' || i === 0 || line.length !== 9) continue;
+        //  ^ Label     ^ Label    ^ Invalid
 
-            // Establish sentiment value
-            var emoji = String.fromCodePoint(line[1]);
-            var occurences = line[2];
-            var negCount = line[4];
-            var posCount = line[6];
-            var score = (posCount / occurences) - (negCount / occurences);
-            var sentiment = Math.floor(5 * score);
+        // Establish sentiment value
+        const emoji = String.fromCodePoint(line[1]);
+        const occurences = line[2];
+        const negCount = line[4];
+        const posCount = line[6];
+        const score = posCount / occurences - negCount / occurences;
+        const sentiment = Math.floor(5 * score);
 
-            // Validate score
-            if (Number.isNaN(sentiment)) continue;
-            if (sentiment === 0) continue;
+        // Validate score
+        if (Number.isNaN(sentiment) || sentiment === 0) continue;
 
-            // Add to hash
-            hash[emoji] = sentiment;
-        }
-
-        callback(null, hash);
-    });
-}
+        // Add to hash
+        hash[emoji] = sentiment;
+    }
+    return hash;
+};
 
 /**
- * Write sentiment score hash to disk.
+ * Writes sentiment score hash to disk.
  * @param  {object}   hash     Result hash
- * @param  {Function} callback Callback
- * @return {void}
+ * @return {object}   hash     Result hash
  */
-function finish(hash, callback) {
-    var result = JSON.stringify(hash, null, 4);
-    fs.writeFile(RESULT_PATH, result, function (err) {
-        if (err) return callback(err);
-        callback(null, hash);
-    });
-}
+const writeJSON = async hash => {
+    const result = JSON.stringify(hash, null, 4);
+    await fs.writeFileSync(RESULT_PATH, result);
+    process.stdout.write(`Complete: ${Object.keys(hash).length} entries.\n`);
+};
 
-// Execute build process
-async.waterfall([
-    function (cb) {
-        cb(null, {});
-    },
-    processEmoji,
-    finish
-], function(err, result) {
-    if (err) throw new Error(err);
-    process.stderr.write(
-        'Complete: ' +
-        Object.keys(result).length +
-        ' entries.\n'
-    );
-});
+/**
+ * Executes build process.
+ * @return {undefined}
+ */
+const build = async () => {
+    try {
+        const hash = await processEmoji();
+        writeJSON(hash);
+    } catch (e) {
+        process.stderr.write(`${e.toString()}\n`);
+    }
+};
+build();
diff --git a/languages/en/index.js b/languages/en/index.js
index 46e0f91..207c1f6 100644
--- a/languages/en/index.js
+++ b/languages/en/index.js
@@ -1,4 +1,7 @@
+const labels = require('./labels.json');
+const scoringStrategy = require('./scoring-strategy');
+
 module.exports = {
-    labels: require('./labels.json'),
-    scoringStrategy: require('./scoring-strategy')
+    labels,
+    scoringStrategy
 };
diff --git a/languages/en/scoring-strategy.js b/languages/en/scoring-strategy.js
index d9a09ca..e4c05b3 100644
--- a/languages/en/scoring-strategy.js
+++ b/languages/en/scoring-strategy.js
@@ -1,13 +1,15 @@
-var negators = require('./negators.json');
+const negators = require('./negators.json');
 
-module.exports = {
-    apply: function(tokens, cursor, tokenScore) {
-        if (cursor > 0) {
-            var prevtoken = tokens[cursor - 1];
-            if (negators[prevtoken]) {
-                tokenScore = -tokenScore;
-            }
+const apply = (tokens, cursor, tokenScore) => {
+    if (cursor > 0) {
+        const prevtoken = tokens[cursor - 1];
+        if (negators[prevtoken]) {
+            tokenScore = -tokenScore;
         }
-        return tokenScore;
     }
+    return tokenScore;
+};
+
+module.exports = {
+    apply
 };
diff --git a/lib/index.js b/lib/index.js
index ff8a672..05e4e9a 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -1,98 +1,97 @@
-var tokenize = require('./tokenize');
-var languageProcessor = require('./language-processor');
+const tokenize = require('./tokenize');
+const languageProcessor = require('./language-processor');
 
-/**
- * Constructor
- * @param {Object} options - Instance options
- */
-var Sentiment = function (options) {
-    this.options = options;
-};
-
-/**
- * Registers the specified language
- *
- * @param {String} languageCode
- *     - Two-digit code for the language to register
- * @param {Object} language
- *     - The language module to register
- */
-Sentiment.prototype.registerLanguage = function (languageCode, language) {
-    languageProcessor.addLanguage(languageCode, language);
-};
-
-/**
- * Performs sentiment analysis on the provided input 'phrase'.
- *
- * @param {String} phrase
- *     - Input phrase
- * @param {Object} opts
- *     - Options
- * @param {Object} opts.language
- *     - Input language code (2 digit code), defaults to 'en'
- * @param {Object} opts.extras
- *     - Optional sentiment additions to AFINN (hash k/v pairs)
- * @param {function} callback
- *     - Optional callback
- * @return {Object}
- */
-Sentiment.prototype.analyze = function (phrase, opts, callback) {
-    // Parse arguments
-    if (typeof phrase === 'undefined') phrase = '';
-    if (typeof opts === 'function') {
-        callback = opts;
-        opts = {};
+class Sentiment {
+    /**
+     * Represents a Sentiment.
+     * @constructor
+     * @param {Object} options - Instance options.
+     */
+    constructor(options) {
+        this.options = options;
     }
-    opts = opts || {};
-
-    var languageCode = opts.language || 'en';
-    var labels = languageProcessor.getLabels(languageCode);
-
-    // Merge extra labels
-    if (typeof opts.extras === 'object') {
-        labels = Object.assign(labels, opts.extras);
+    /**
+     * Registers the specified language.
+     * @param {string} languageCode - Two-digit code for the language to
+     *                              register.
+     * @param {object} language - The language module to register.
+     */
+    registerLanguage(languageCode, language) {
+        languageProcessor.addLanguage(languageCode, language);
     }
+    /**
+     * Performs sentiment analysis on the provided input 'phrase'.
+     * @param {string} phrase - Input phrase
+     * @param {object} opts - Options
+     * @param {object} opts.language - Input language code (2 digit code),
+     *                               defaults to 'en'
+     * @param {object} opts.extras - Optional sentiment additions to AFINN
+     *                             (hash k/v pairs)
+     * @param {function} callback - Optional callback
+     * @return {object}
+     */
+    analyze(phrase = '', opts = { language: 'en' }, callback) {
+        // Storage objects
+        const tokens = tokenize(phrase);
+        let score = 0;
+        let words = [];
+        let positive = [];
+        let negative = [];
 
-    // Storage objects
-    var tokens      = tokenize(phrase),
-        score       = 0,
-        words       = [],
-        positive    = [],
-        negative    = [];
+        // Parse arguments
+        if (typeof opts === 'function') {
+            callback = opts;
+            opts = {};
+        }
 
-    // Iterate over tokens
-    var i = tokens.length;
-    while (i--) {
-        var obj = tokens[i];
-        if (!labels.hasOwnProperty(obj)) continue;
-        words.push(obj);
+        const languageCode = opts.language;
+        let labels = languageProcessor.getLabels(languageCode);
 
-        // Apply scoring strategy
-        var tokenScore = labels[obj];
-        // eslint-disable-next-line max-len
-        tokenScore = languageProcessor.applyScoringStrategy(languageCode, tokens, i, tokenScore);
-        if (tokenScore > 0) positive.push(obj);
-        if (tokenScore < 0) negative.push(obj);
-        score += tokenScore;
-    }
+        // Merge extra labels
+        if (typeof opts.extras === 'object') {
+            labels = Object.assign(labels, opts.extras);
+        }
+
+        // Iterate over tokens
+        let i = tokens.length;
+        while (i--) {
+            const obj = tokens[i];
+            if (!labels.hasOwnProperty(obj)) continue;
+            words = words.concat(obj);
+            // Apply scoring strategy
+            const tokenScore = languageProcessor.applyScoringStrategy(
+                languageCode,
+                tokens,
+                i,
+                labels[obj]
+            );
+            if (tokenScore > 0) {
+                positive = positive.concat(obj);
+            }
+            if (tokenScore < 0) {
+                negative = negative.concat(obj);
+            }
+            score += tokenScore;
+        }
 
-    var result = {
-        score:          score,
-        comparative:    tokens.length > 0 ? score / tokens.length : 0,
-        tokens:         tokens,
-        words:          words,
-        positive:       positive,
-        negative:       negative
-    };
+        const result = {
+            score,
+            comparative: tokens.length > 0 ? score / tokens.length : 0,
+            tokens,
+            words,
+            positive,
+            negative
+        };
 
-    // Handle optional async interface
-    if (typeof callback === 'function') {
-        process.nextTick(function () {
-            callback(null, result);
-        });
-    } else {
-        return result;
+        // Handle optional async interface
+        if (typeof callback === 'function') {
+            process.nextTick(() => {
+                callback(null, result);
+            });
+        } else {
+            return result;
+        }
     }
-};
+}
 
 module.exports = Sentiment;
diff --git a/lib/language-processor.js b/lib/language-processor.js
index fe373de..504fd74 100644
--- a/lib/language-processor.js
+++ b/lib/language-processor.js
@@ -1,89 +1,80 @@
-var emojis = require('../build/emoji.json');
-
+const emojis = require('../build/emoji.json');
 // English is loaded by default
-var enLanguage = require('../languages/en/index');
+const enLanguage = require('../languages/en/index');
 // Add emojis
 Object.assign(enLanguage.labels, emojis);
 
 // Cache loaded languages
-var languages = {
+const languages = {
     en: enLanguage
 };
 
-module.exports = {
-
-    /**
-     * Registers the specified language
-     *
-     * @param {String} languageCode
-     *     - Two-digit code for the language to register
-     * @param {Object} language
-     *     - The language module to register
-     */
-    addLanguage: function (languageCode, language) {
-        if (!language.labels) {
-            throw new Error('language.labels must be defined!');
-        }
-        // Add emojis
-        Object.assign(language.labels, emojis);
-        languages[languageCode] = language;
-    },
-
-    /**
-     * Retrieves a language object from the cache,
-     * or tries to load it from the set of supported languages
-     *
-     * @param {String} languageCode - Two-digit code for the language to fetch
-     */
-    getLanguage: function(languageCode) {
-        if (!languageCode) {
-            // Default to english if no language was specified
-            return languages.en;
-        }
-        if (!languages[languageCode]) {
-            // Try to load specified language
-            try {
-                // eslint-disable-next-line max-len
-                var language = require('../languages/' + languageCode + '/index');
-                // Add language to in-memory cache
-                this.addLanguage(languageCode, language);
-            } catch (err) {
-                throw new Error('No language found: ' + languageCode);
-            }
+const defaultScoringStrategy = {
+    apply: (tokens, cursor, tokenScore) => tokenScore
+};
+/**
+ * Registers the specified language.
+ * @param  {string} languageCode - Two-digit code for the language to register.
+ * @param  {object} language - The language module to register.
+ * @return {undefined}
+ */
+const addLanguage = (languageCode, language) => {
+    if (!language.labels) {
+        throw new Error('language.labels must be defined!');
+    }
+    // Add emojis
+    Object.assign(language.labels, emojis);
+    languages[languageCode] = language;
+};
+/**
+ * Retrieves a language object from the cache, or tries to load it from the set
+ *     of supported languages.
+ * @param  {string} languageCode - Two-digit code for the language to fetch.
+ * @return {undefined}
+ */
+const getLanguage = languageCode => {
+    if (!languageCode) {
+        // Default to english if no language was specified
+        return languages.en;
+    }
+    if (!languages[languageCode]) {
+        // Try to load specified language
+        try {
+            const language = require(`../languages/${languageCode}/index`);
+            // Add language to in-memory cache
+            addLanguage(languageCode, language);
+        } catch (err) {
+            throw new Error('No language found: ' + languageCode);
         }
-        return languages[languageCode];
-    },
-
-    /**
-     * Returns AFINN-165 weighted labels for the specified language
-     *
-     * @param {String} languageCode - Two-digit language code
-     * @return {Object}
-     */
-    getLabels: function(languageCode) {
-        var language = this.getLanguage(languageCode);
-        return language.labels;
-    },
-
-    /**
-     * Applies a scoring strategy for the current token
-     *
-     * @param {String} languageCode - Two-digit language code
-     * @param {Array} tokens - Tokens of the phrase to analyze
-     * @param {int} cursor - Cursor of the current token being analyzed
-     * @param {int} tokenScore - The score of the current token being analyzed
-     */
-    applyScoringStrategy: function(languageCode, tokens, cursor, tokenScore) {
-        var language = this.getLanguage(languageCode);
-        // Fallback to default strategy if none was specified
-        // eslint-disable-next-line max-len
-        var scoringStrategy = language.scoringStrategy || defaultScoringStrategy;
-        return scoringStrategy.apply(tokens, cursor, tokenScore);
     }
+    return languages[languageCode];
+};
+/**
+ * Returns AFINN-165 weighted labels for the specified language.
+ * @param  {string} languageCode - Two-digit language code.
+ * @return {object}
+ */
+const getLabels = languageCode => {
+    const { labels } = getLanguage(languageCode);
+    return labels;
+};
+/**
+ * Applies a scoring strategy for the current token.
+ * @param  {string} languageCode - Two-digit language code.
+ * @param  {array} Tokens - Tokens of the phase to analyze.
+ * @param  {int} cursor - Cursor of the current token being analyzed.
+ * @param  {int} tokenScore - The score of the current token being analyzed.
+ */
+const applyScoringStrategy = (languageCode, tokens, cursor, tokenScore) => {
+    const language = getLanguage(languageCode);
+    // Fallback to default strategy if none was specified
+    const scoringStrategy = language.scoringStrategy || defaultScoringStrategy;
+    return scoringStrategy.apply(tokens, cursor, tokenScore);
 };
 
-var defaultScoringStrategy = {
-    apply: function(tokens, cursor, tokenScore) {
-        return tokenScore;
-    }
+module.exports = {
+    addLanguage,
+    getLanguage,
+    getLabels,
+    applyScoringStrategy
 };
diff --git a/lib/tokenize.js b/lib/tokenize.js
index 6ac47a4..6b25d98 100644
--- a/lib/tokenize.js
+++ b/lib/tokenize.js
@@ -1,14 +1,15 @@
 /*eslint no-useless-escape: "off"*/
 
 /**
- * Remove special characters and return an array of tokens (words).
- * @param  {string} input Input string
- * @return {array}        Array of tokens
+ * Removes special characters and return an array of tokens (words).
+ * @param  {string} input Input string.
+ * @return {array}       Array of tokens.
  */
-module.exports = function(input) {
-    return input
+const tokenize = input =>
+    input
         .toLowerCase()
         .replace(/\n/g, ' ')
         .replace(/[.,\/#!$%\^&\*;:{}=_`\"~()]/g, '')
         .split(' ');
-};
+
+module.exports = tokenize;
diff --git a/package.json b/package.json
index c10751d..f997c9c 100644
--- a/package.json
+++ b/package.json
@@ -28,7 +28,6 @@
   },
   "devDependencies": {
     "Sentimental": "1.0.1",
-    "async": "^2.1.5",
     "benchmark": "^2.1.0",
     "eslint": "^4.6.1",
     "mock-require": "^3.0.1",
@@ -37,4 +36,4 @@
   "engines": {
     "node": ">=8.0"
   }
-}
+}
\ No newline at end of file
diff --git a/test/benchmark/performance.js b/test/benchmark/performance.js
index caa9499..71f1a02 100644
--- a/test/benchmark/performance.js
+++ b/test/benchmark/performance.js
@@ -8,36 +8,36 @@
 /**
  * Dependencies
  */
-var Benchmark = require('benchmark');
-var suite = new Benchmark.Suite();
+const Benchmark = require('benchmark');
+const suite = new Benchmark.Suite();
 
-var Sentiment = require('../../lib/index');
-var sentiment = new Sentiment();
-var sentimental = require('Sentimental');
+const Sentiment = require('../../lib/index');
+const sentiment = new Sentiment();
+const sentimental = require('Sentimental');
 
 /**
  * Test data
  */
-var stringShort = 'This cat is totally awesome';
-var stringLong = require('../fixtures/corpus');
+const stringShort = 'This cat is totally awesome';
+const stringLong = require('../fixtures/corpus');
 
 /**
  * Setup
  */
 suite
-    .add('sentiment (Latest) - Short ', function () {
+    .add('sentiment (Latest)  - Short', () => {
         sentiment.analyze(stringShort);
     })
-    .add('sentiment (Latest) - Long  ', function () {
+    .add('sentiment (Latest)  - Long ', () => {
         sentiment.analyze(stringLong);
     })
-    .add('Sentimental (1.0.1) - Short', function () {
+    .add('Sentimental (1.0.1) - Short', () => {
         sentimental.analyze(stringShort);
     })
-    .add('Sentimental (1.0.1) - Long ', function () {
+    .add('Sentimental (1.0.1) - Long ', () => {
         sentimental.analyze(stringLong);
     })
-    .on('cycle', function (event) {
+    .on('cycle', event => {
         process.stdout.write(String(event.target) + '\n');
     })
     .run({
diff --git a/test/benchmark/validate.js b/test/benchmark/validate.js
index 7a7d0ff..793add2 100644
--- a/test/benchmark/validate.js
+++ b/test/benchmark/validate.js
@@ -1,26 +1,26 @@
-var Sentiment = require('../../lib/index');
-var sentiment = new Sentiment();
+const Sentiment = require('../../lib/index');
+const sentiment = new Sentiment();
 
-var amazon = require('../fixtures/amazon.json');
-var imdb = require('../fixtures/imdb.json');
-var yelp = require('../fixtures/yelp.json');
+const amazon = require('../fixtures/amazon.json');
+const imdb = require('../fixtures/imdb.json');
+const yelp = require('../fixtures/yelp.json');
 
-function validate (set) {
+function validate(set) {
     // Storage object
-    var obj = {
+    const obj = {
         pass: 0,
         fail: 0
     };
 
     // Iterate over each word/class pair in the dataset
     for (var i in set) {
-        var score = sentiment.analyze(set[i].text).comparative;
+        const score = sentiment.analyze(set[i].text).comparative;
         if (set[i].class === 0) {
-            if (score >= 0) obj.fail++;
-            if (score < 0) obj.pass++;
+            if (score >= 0) ++obj.fail;
+            if (score < 0) ++obj.pass;
         } else {
-            if (score >= 0) obj.pass++;
-            if (score < 0) obj.fail++;
+            if (score >= 0) ++obj.pass;
+            if (score < 0) ++obj.fail;
         }
     }
 
@@ -28,6 +28,6 @@ function validate (set) {
     return obj.pass / (obj.pass + obj.fail);
 }
 
-process.stdout.write('Amazon accuracy: ' + validate(amazon) + '\n');
-process.stdout.write('IMDB accuracy: ' + validate(imdb) + '\n');
-process.stdout.write('Yelp accuracy: ' + validate(yelp) + '\n');
+process.stdout.write(`Amazon accuracy: ${validate(amazon)}\n`);
+process.stdout.write(`  IMDB accuracy: ${validate(imdb)}\n`);
+process.stdout.write(`  Yelp accuracy: ${validate(yelp)}\n`);
diff --git a/test/fixtures/fuzz.js b/test/fixtures/fuzz.js
index 5d1e453..1b0b485 100644
--- a/test/fixtures/fuzz.js
+++ b/test/fixtures/fuzz.js
@@ -1,33 +1,27 @@
-function rand (limit) {
-    return Math.floor(Math.random() * limit);
-}
+const rand = limit => Math.floor(Math.random() * limit);
 
-function createRandomWord (length) {
-    var consonants = 'bcdfghjklmnpqrstvwxyz!@#$%^&*()_+":;\'?><~`';
-    var vowels = 'aeiou';
-    var word = '';
-
-    // Split
-    consonants = consonants.split('');
-    vowels = vowels.split('');
+const createRandomWord = length => {
+    const consonants = 'bcdfghjklmnpqrstvwxyz!@#$%^&*()_+":;\'?><~`'.split('');
+    const vowels = 'aeiou'.split('');
+    let word = '';
 
     // Create word
-    for (var i = 0; i < length / 2; i++) {
-        var randConsonant = consonants[rand(consonants.length)];
-        var randVowel = vowels[rand(vowels.length)];
-        
-        word += (i===0) ? randConsonant.toUpperCase() : randConsonant;
-        word += i*2<length-1 ? randVowel : '';
-    }
+    for (let i = 0; i < length / 2; i++) {
+        const randConsonant = consonants[rand(consonants.length)];
+        const randVowel = vowels[rand(vowels.length)];
 
+        word += i === 0 ? randConsonant.toUpperCase() : randConsonant;
+        word += i * 2 < length - 1 ? randVowel : '';
+    }
     return word;
-}
+};
 
-module.exports = function (length) {
-    var words = [];
-    for (var i = 0; i < length; i++) {
+const fuzz = length => {
+    const words = [];
+    for (let i = 0; i < length; i++) {
         words.push(createRandomWord(rand(20)));
     }
-
     return words.join(' ');
 };
+
+module.exports = fuzz;
diff --git a/test/integration/add_lang.js b/test/integration/add_lang.js
index b029c5c..96ccb59 100644
--- a/test/integration/add_lang.js
+++ b/test/integration/add_lang.js
@@ -1,9 +1,9 @@
-var test = require('tap').test;
-var Sentiment = require('../../lib/index');
-var sentiment = new Sentiment();
+const test = require('tap').test;
+const Sentiment = require('../../lib/index');
+const sentiment = new Sentiment();
 
-test('adding a language with no labels attribute should throw', function (t) {
-    t.throws(function () {
+test('adding a language with no labels attribute should throw', t => {
+    t.throws(() => {
         sentiment.registerLanguage('xx', {});
     }, new Error('language.labels must be defined!'));
     t.end();
diff --git a/test/integration/async_inject.js b/test/integration/async_inject.js
index 59077b8..772f4cd 100644
--- a/test/integration/async_inject.js
+++ b/test/integration/async_inject.js
@@ -1,14 +1,14 @@
-var test = require('tap').test;
-var Sentiment = require('../../lib/index');
-var sentiment = new Sentiment();
+const test = require('tap').test;
+const Sentiment = require('../../lib/index');
+const sentiment = new Sentiment();
 
-var input = 'This is so cool';
-var options = {
-    extras: { 'cool': 100 }
+const input = 'This is so cool';
+const options = {
+    extras: { cool: 100 }
 };
 
-sentiment.analyze(input, options, function (err, result) {
-    test('asynchronous inject', function (t) {
+sentiment.analyze(input, options, (err, result) => {
+    test('asynchronous inject', t => {
         t.type(result, 'object');
         t.equal(result.score, 100);
         t.equal(result.comparative, 25);
diff --git a/test/integration/async_negative.js b/test/integration/async_negative.js
index ac60a27..17a82bd 100644
--- a/test/integration/async_negative.js
+++ b/test/integration/async_negative.js
@@ -1,11 +1,11 @@
-var test = require('tap').test;
-var Sentiment = require('../../lib/index');
-var sentiment = new Sentiment();
+const test = require('tap').test;
+const Sentiment = require('../../lib/index');
+const sentiment = new Sentiment();
 
-var input = 'Hey you worthless scumbag';
+const input = 'Hey you worthless scumbag';
 
-sentiment.analyze(input, function (err, result) {
-    test('asynchronous negative', function (t) {
+sentiment.analyze(input, (err, result) => {
+    test('asynchronous negative', t => {
         t.type(result, 'object');
         t.equal(result.score, -6);
         t.equal(result.comparative, -1.5);
diff --git a/test/integration/async_negative_text_and_emoji.js b/test/integration/async_negative_text_and_emoji.js
index dc5c9d1..eed9465 100644
--- a/test/integration/async_negative_text_and_emoji.js
+++ b/test/integration/async_negative_text_and_emoji.js
@@ -1,11 +1,11 @@
-var test = require('tap').test;
-var Sentiment = require('../../lib/index');
-var sentiment = new Sentiment();
+const test = require('tap').test;
+const Sentiment = require('../../lib/index');
+const sentiment = new Sentiment();
 
-var input = 'Hey you worthless scumbag 😦';
+const input = 'Hey you worthless scumbag 😦';
 
-sentiment.analyze(input, function (err, result) {
-    test('asynchronous negative text and emoji', function (t) {
+sentiment.analyze(input, (err, result) => {
+    test('asynchronous negative text and emoji', t => {
         t.type(result, 'object');
         t.equal(result.score, -8);
         t.equal(result.comparative, -1.6);
diff --git a/test/integration/async_positive.js b/test/integration/async_positive.js
index afb2f0a..94cf751 100644
--- a/test/integration/async_positive.js
+++ b/test/integration/async_positive.js
@@ -1,11 +1,11 @@
-var test = require('tap').test;
-var Sentiment = require('../../lib/index');
-var sentiment = new Sentiment();
+const test = require('tap').test;
+const Sentiment = require('../../lib/index');
+const sentiment = new Sentiment();
 
-var input = 'This is so cool';
+const input = 'This is so cool';
 
-sentiment.analyze(input, function (err, result) {
-    test('asynchronous positive', function (t) {
+sentiment.analyze(input, (err, result) => {
+    test('asynchronous positive', t => {
         t.type(result, 'object');
         t.equal(result.score, 1);
         t.equal(result.comparative, 0.25);
diff --git a/test/integration/async_positive_text_and_emoji.js b/test/integration/async_positive_text_and_emoji.js
index abf18d5..8b1d18b 100644
--- a/test/integration/async_positive_text_and_emoji.js
+++ b/test/integration/async_positive_text_and_emoji.js
@@ -1,11 +1,11 @@
-var test = require('tap').test;
-var Sentiment = require('../../lib/index');
-var sentiment = new Sentiment();
+const test = require('tap').test;
+const Sentiment = require('../../lib/index');
+const sentiment = new Sentiment();
 
-var input = 'This is so cool 😃';
+const input = 'This is so cool 😃';
 
-sentiment.analyze(input, function (err, result) {
-    test('asynchronous positive text and emoji', function (t) {
+sentiment.analyze(input, (err, result) => {
+    test('asynchronous positive text and emoji', t => {
         t.type(result, 'object');
         t.equal(result.score, 3);
         t.equal(result.comparative, 0.6);
diff --git a/test/integration/custom_lang.js b/test/integration/custom_lang.js
index c916790..3dc4598 100644
--- a/test/integration/custom_lang.js
+++ b/test/integration/custom_lang.js
@@ -1,15 +1,15 @@
-var test = require('tap').test;
-var Sentiment = require('../../lib/index');
-var sentiment = new Sentiment();
+const test = require('tap').test;
+const Sentiment = require('../../lib/index');
+const sentiment = new Sentiment();
 
-var input = 'This is so cool';
+const input = 'This is so cool';
 
 sentiment.registerLanguage('xx', {
-    labels: { 'cool': 5 }
+    labels: { cool: 5 }
 });
 
-sentiment.analyze(input, { language: 'xx' }, function (err, result) {
-    test('asynchronous positive', function (t) {
+sentiment.analyze(input, { language: 'xx' }, (err, result) => {
+    test('asynchronous positive', t => {
         t.type(result, 'object');
         t.equal(result.score, 5);
         t.equal(result.comparative, 1.25);
diff --git a/test/integration/gh_12.js b/test/integration/gh_12.js
index 1d8f01a..90f42fc 100644
--- a/test/integration/gh_12.js
+++ b/test/integration/gh_12.js
@@ -1,11 +1,11 @@
-var test = require('tap').test;
-var Sentiment = require('../../lib/index');
-var sentiment = new Sentiment();
+const test = require('tap').test;
+const Sentiment = require('../../lib/index');
+const sentiment = new Sentiment();
 
-var input = 'self-deluded';
-var result = sentiment.analyze(input);
+const input = 'self-deluded';
+const result = sentiment.analyze(input);
 
-test('synchronous positive', function (t) {
+test('synchronous positive', t => {
     t.type(result, 'object');
     t.equal(result.score, -2);
     t.equal(result.comparative, -2);
diff --git a/test/integration/gh_13.js b/test/integration/gh_13.js
index 2903cc0..9e53cda 100644
--- a/test/integration/gh_13.js
+++ b/test/integration/gh_13.js
@@ -1,11 +1,11 @@
-var test = require('tap').test;
-var Sentiment = require('../../lib/index');
-var sentiment = new Sentiment();
+const test = require('tap').test;
+const Sentiment = require('../../lib/index');
+const sentiment = new Sentiment();
 
-var input = 'constructor';
-var result = sentiment.analyze(input);
+const input = 'constructor';
+const result = sentiment.analyze(input);
 
-test('synchronous positive', function (t) {
+test('synchronous positive', t => {
     t.type(result, 'object');
     t.equal(result.score, 0);
     t.equal(result.comparative, 0);
diff --git a/test/integration/gh_85.js b/test/integration/gh_85.js
index b3ea090..1dca164 100644
--- a/test/integration/gh_85.js
+++ b/test/integration/gh_85.js
@@ -1,11 +1,11 @@
-var test = require('tap').test;
-var Sentiment = require('../../lib/index');
-var sentiment = new Sentiment();
+const test = require('tap').test;
+const Sentiment = require('../../lib/index');
+const sentiment = new Sentiment();
 
-var input = 'i\'ll be there soon';
-var result = sentiment.analyze(input);
+const input = 'i\'ll be there soon';
+const result = sentiment.analyze(input);
 
-test('synchronous positive', function (t) {
+test('synchronous positive', t => {
     t.type(result, 'object');
     t.equal(result.score, 0);
     t.equal(result.comparative, 0);
diff --git a/test/integration/supported_lang.js b/test/integration/supported_lang.js
index 5db1679..493d57d 100644
--- a/test/integration/supported_lang.js
+++ b/test/integration/supported_lang.js
@@ -1,17 +1,17 @@
-var test = require('tap').test;
-var Sentiment = require('../../lib/index');
-var sentiment = new Sentiment();
-var mock = require('mock-require');
+const test = require('tap').test;
+const Sentiment = require('../../lib/index');
+const sentiment = new Sentiment();
+const mock = require('mock-require');
+const input = 'This is so cool';
 
 // Mock a supported language
 mock('../../languages/yy/index', {
-    labels: { 'cool': 20 }
+    labels: { cool: 20 }
 });
 
-var input = 'This is so cool';
-var result = sentiment.analyze(input, { language: 'yy' });
+const result = sentiment.analyze(input, { language: 'yy' });
 
-test('synchronous positive', function (t) {
+test('synchronous positive', t => {
     t.type(result, 'object');
     t.equal(result.score, 20);
     t.equal(result.comparative, 5);
diff --git a/test/integration/sync_corpus.js b/test/integration/sync_corpus.js
index 72d45ea..b6f17ee 100644
--- a/test/integration/sync_corpus.js
+++ b/test/integration/sync_corpus.js
@@ -1,12 +1,12 @@
-var test = require('tap').test;
-var corpus = require('../fixtures/corpus');
-var Sentiment = require('../../lib/index');
-var sentiment = new Sentiment();
+const test = require('tap').test;
+const corpus = require('../fixtures/corpus');
+const Sentiment = require('../../lib/index');
+const sentiment = new Sentiment();
 
-var dataset = corpus;
-var result = sentiment.analyze(dataset);
+const dataset = corpus;
+const result = sentiment.analyze(dataset);
 
-test('synchronous corpus', function (t) {
+test('synchronous corpus', t => {
     t.type(result, 'object');
     t.equal(result.score, -3);
     t.equal(result.tokens.length, 1416);
diff --git a/test/integration/sync_fuzz.js b/test/integration/sync_fuzz.js
index 9a94d53..5b1bca7 100644
--- a/test/integration/sync_fuzz.js
+++ b/test/integration/sync_fuzz.js
@@ -1,11 +1,11 @@
-var test = require('tap').test;
-var fuzz = require('../fixtures/fuzz');
-var Sentiment = require('../../lib/index');
-var sentiment = new Sentiment();
+const test = require('tap').test;
+const fuzz = require('../fixtures/fuzz');
+const Sentiment = require('../../lib/index');
+const sentiment = new Sentiment();
 
-var input = fuzz(1000);
+const input = fuzz(1000);
 
-test('synchronous fuzz', function (t) {
+test('synchronous fuzz', t => {
     t.type(sentiment.analyze(input), 'object');
     t.end();
 });
diff --git a/test/integration/sync_inject.js b/test/integration/sync_inject.js
index c8dd90c..9f4fab8 100644
--- a/test/integration/sync_inject.js
+++ b/test/integration/sync_inject.js
@@ -1,15 +1,15 @@
-var test = require('tap').test;
-var Sentiment = require('../../lib/index');
-var sentiment = new Sentiment();
+const test = require('tap').test;
+const Sentiment = require('../../lib/index');
+const sentiment = new Sentiment();
 
-var input = 'This is so cool';
-var options = {
-    extras: { 'cool': 100 }
+const input = 'This is so cool';
+const options = {
+    extras: { cool: 100 }
 };
 
-var result = sentiment.analyze(input, options);
+const result = sentiment.analyze(input, options);
 
-test('synchronous inject', function (t) {
+test('synchronous inject', t => {
     t.type(result, 'object');
     t.equal(result.score, 100);
     t.equal(result.comparative, 25);
diff --git a/test/integration/sync_negation.js b/test/integration/sync_negation.js
index 0635a9b..28674df 100644
--- a/test/integration/sync_negation.js
+++ b/test/integration/sync_negation.js
@@ -1,11 +1,11 @@
-var test = require('tap').test;
-var Sentiment = require('../../lib/index');
-var sentiment = new Sentiment();
+const test = require('tap').test;
+const Sentiment = require('../../lib/index');
+const sentiment = new Sentiment();
 
-var input = 'I don\'t hate you';
-var result = sentiment.analyze(input);
+const input = 'I don\'t hate you';
+const result = sentiment.analyze(input);
 
-test('synchronous negation', function (t) {
+test('synchronous negation', t => {
     t.type(result, 'object');
     t.equal(result.score, 3);
     t.equal(result.comparative, 0.75);
diff --git a/test/integration/sync_negative.js b/test/integration/sync_negative.js
index cb6019a..7b153f2 100644
--- a/test/integration/sync_negative.js
+++ b/test/integration/sync_negative.js
@@ -1,11 +1,11 @@
-var test = require('tap').test;
-var Sentiment = require('../../lib/index');
-var sentiment = new Sentiment();
+const test = require('tap').test;
+const Sentiment = require('../../lib/index');
+const sentiment = new Sentiment();
 
-var input = 'Hey you worthless scumbag';
-var result = sentiment.analyze(input);
+const input = 'Hey you worthless scumbag';
+const result = sentiment.analyze(input);
 
-test('synchronous negative', function (t) {
+test('synchronous negative', t => {
     t.type(result, 'object');
     t.equal(result.score, -6);
     t.equal(result.comparative, -1.5);
diff --git a/test/integration/sync_negative_text_and_emoji.js b/test/integration/sync_negative_text_and_emoji.js
index 4514f7f..5e3cdf8 100644
--- a/test/integration/sync_negative_text_and_emoji.js
+++ b/test/integration/sync_negative_text_and_emoji.js
@@ -1,11 +1,11 @@
-var test = require('tap').test;
-var Sentiment = require('../../lib/index');
-var sentiment = new Sentiment();
+const test = require('tap').test;
+const Sentiment = require('../../lib/index');
+const sentiment = new Sentiment();
 
-var input = 'Hey you worthless scumbag 😦';
-var result = sentiment.analyze(input);
+const input = 'Hey you worthless scumbag 😦';
+const result = sentiment.analyze(input);
 
-test('synchronous negative with emoji', function (t) {
+test('synchronous negative with emoji', t => {
     t.type(result, 'object');
     t.equal(result.score, -8);
     t.equal(result.comparative, -1.6);
diff --git a/test/integration/sync_positive.js b/test/integration/sync_positive.js
index 35260a0..0b485ab 100644
--- a/test/integration/sync_positive.js
+++ b/test/integration/sync_positive.js
@@ -1,11 +1,11 @@
-var test = require('tap').test;
-var Sentiment = require('../../lib/index');
-var sentiment = new Sentiment();
+const test = require('tap').test;
+const Sentiment = require('../../lib/index');
+const sentiment = new Sentiment();
 
-var input = 'This is so cool';
-var result = sentiment.analyze(input);
+const input = 'This is so cool';
+const result = sentiment.analyze(input);
 
-test('synchronous positive', function (t) {
+test('synchronous positive', t => {
     t.type(result, 'object');
     t.equal(result.score, 1);
     t.equal(result.comparative, 0.25);
diff --git a/test/integration/sync_positive_text_and_emoji.js b/test/integration/sync_positive_text_and_emoji.js
index f9bf464..4e950df 100644
--- a/test/integration/sync_positive_text_and_emoji.js
+++ b/test/integration/sync_positive_text_and_emoji.js
@@ -1,11 +1,11 @@
-var test = require('tap').test;
-var Sentiment = require('../../lib/index');
-var sentiment = new Sentiment();
+const test = require('tap').test;
+const Sentiment = require('../../lib/index');
+const sentiment = new Sentiment();
 
-var input = 'This is so cool 😃';
-var result = sentiment.analyze(input);
+const input = 'This is so cool 😃';
+const result = sentiment.analyze(input);
 
-test('synchronous positive with emoji', function (t) {
+test('synchronous positive with emoji', t => {
     t.type(result, 'object');
     t.equal(result.score, 3);
     t.equal(result.comparative, 0.6);
diff --git a/test/integration/sync_undefined.js b/test/integration/sync_undefined.js
index 33b91af..608013a 100644
--- a/test/integration/sync_undefined.js
+++ b/test/integration/sync_undefined.js
@@ -1,11 +1,11 @@
-var test = require('tap').test;
-var Sentiment = require('../../lib/index');
-var sentiment = new Sentiment();
+const test = require('tap').test;
+const Sentiment = require('../../lib/index');
+const sentiment = new Sentiment();
 
-var input = undefined;
-var result = sentiment.analyze(input);
+const input = undefined;
+const result = sentiment.analyze(input);
 
-test('synchronous undefined', function (t) {
+test('synchronous undefined', t => {
     t.type(result, 'object');
     t.equal(result.score, 0);
     t.equal(result.comparative, 0);
diff --git a/test/unit/language-processor.js b/test/unit/language-processor.js
index c546da7..a2901a1 100644
--- a/test/unit/language-processor.js
+++ b/test/unit/language-processor.js
@@ -1,7 +1,8 @@
-var test = require('tap').test;
-var languageProcessor = require('../../lib/language-processor');
+const test = require('tap').test;
+const languageProcessor = require('../../lib/language-processor');
+const englishLanguage = require('../../languages/en/index');
 
-test('spec', function (t) {
+test('spec', t => {
     t.type(languageProcessor, 'object');
     t.type(languageProcessor.getLanguage, 'function');
     t.type(languageProcessor.getLabels, 'function');
@@ -9,29 +10,13 @@ test('spec', function (t) {
     t.end();
 });
 
-test('getLanguage', function (t) {
-
-    var englishLanguage = require('../../languages/en/index');
-
-    t.deepEqual(
-        languageProcessor.getLanguage(),
-        englishLanguage
-    );
-
-    t.deepEqual(
-        languageProcessor.getLanguage(null),
-        englishLanguage
-    );
-
-    t.deepEqual(
-        languageProcessor.getLanguage('en'),
-        englishLanguage
-    );
-
-    t.throws(function () {
+test('getLanguage', t => {
+    t.deepEqual(languageProcessor.getLanguage(), englishLanguage);
+    t.deepEqual(languageProcessor.getLanguage(null), englishLanguage);
+    t.deepEqual(languageProcessor.getLanguage('en'), englishLanguage);
+    t.throws(() => {
         // Should throw with unknown language code
         languageProcessor.getLanguage('xx');
     });
-
     t.end();
 });
diff --git a/test/unit/spec.js b/test/unit/spec.js
index 1d14a5c..6b5176f 100644
--- a/test/unit/spec.js
+++ b/test/unit/spec.js
@@ -1,17 +1,20 @@
-var test = require('tap').test;
-var Sentiment = require('../../lib/index');
-var sentiment = new Sentiment();
+const test = require('tap').test;
+const Sentiment = require('../../lib/index');
+const sentiment = new Sentiment();
 
-test('module', function (t) {
+test('module', t => {
     t.type(Sentiment, 'function', 'module is a function');
     t.end();
 });
 
-test('interface', function (t) {
+test('interface', t => {
     t.type(sentiment, 'object', 'instance is an object');
     t.type(sentiment.analyze, 'function', 'sentiment.analyze is a function');
-    // eslint-disable-next-line max-len
-    t.type(sentiment.registerLanguage, 'function', 'sentiment.registerLanguage is a function');
+    t.type(
+        sentiment.registerLanguage,
+        'function',
+        'sentiment.registerLanguage is a function'
+    );
     t.type(sentiment.analyze('test'), 'object');
     t.type(sentiment.analyze('test', { test: 10 }), 'object');
     t.end();
diff --git a/test/unit/tokenize.js b/test/unit/tokenize.js
index 4d8795f..a9f7bf6 100644
--- a/test/unit/tokenize.js
+++ b/test/unit/tokenize.js
@@ -1,48 +1,66 @@
-var test = require('tap').test;
-var tokenize = require('../../lib/tokenize');
+const test = require('tap').test;
+const tokenize = require('../../lib/tokenize');
 
-test('spec', function (t) {
+test('spec', t => {
     t.type(tokenize, 'function');
     t.type(tokenize('foo'), 'object');
     t.equal(tokenize('foo bar').length, 2);
 
-    t.throws(function () {
+    t.throws(() => {
         tokenize(123);
     });
-    t.throws(function () {
+    t.throws(() => {
         tokenize({});
     });
-    t.throws(function () {
+    t.throws(() => {
         tokenize([]);
     });
 
     t.end();
 });
 
-test('english', function (t) {
-    t.deepEqual(
-        tokenize('The cat went over the wall.'),
-        ['the', 'cat', 'went', 'over', 'the', 'wall']
-    );
-    t.deepEqual(
-        tokenize('That\'ll cause problems for the farmer\'s pigs'),
-        ['that\'ll', 'cause', 'problems', 'for', 'the', 'farmer\'s', 'pigs']
-    );
+test('english', t => {
+    t.deepEqual(tokenize('The cat went over the wall.'), [
+        'the',
+        'cat',
+        'went',
+        'over',
+        'the',
+        'wall'
+    ]);
+    t.deepEqual(tokenize('That\'ll cause problems for the farmer\'s pigs'), [
+        'that\'ll',
+        'cause',
+        'problems',
+        'for',
+        'the',
+        'farmer\'s',
+        'pigs'
+    ]);
     t.end();
 });
 
-test('diacritic', function (t) {
-    t.deepEqual(
-        tokenize('This approach is naïve.'),
-        ['this', 'approach', 'is', 'naïve']
-    );
-    t.deepEqual(
-        tokenize('The puppy bowl team was very coöperative.'),
-        ['the', 'puppy', 'bowl', 'team', 'was', 'very', 'coöperative']
-    );
-    t.deepEqual(
-        tokenize('The soufflé was delicious!'),
-        ['the', 'soufflé', 'was', 'delicious']
-    );
+test('diacritic', t => {
+    t.deepEqual(tokenize('This approach is naïve.'), [
+        'this',
+        'approach',
+        'is',
+        'naïve'
+    ]);
+    t.deepEqual(tokenize('The puppy bowl team was very coöperative.'), [
+        'the',
+        'puppy',
+        'bowl',
+        'team',
+        'was',
+        'very',
+        'coöperative'
+    ]);
+    t.deepEqual(tokenize('The soufflé was delicious!'), [
+        'the',
+        'soufflé',
+        'was',
+        'delicious'
+    ]);
     t.end();
 });