diff --git a/.circleci/config.yml b/.circleci/config.yml
index 62fea2b62..95d136980 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -8,7 +8,7 @@ jobs:
 
       # Install development dependencies
       - run: sudo apt-get install python3 python3-pip
-      - run: sudo npm install -g jsonlint eslint htmlhint sass-lint
+      - run: sudo npm install -g jsonlint eslint flow flow-bin htmlhint sass-lint
       - run: sudo pip3 install flake8
 
       # Run tests
@@ -17,6 +17,7 @@ jobs:
       - run: htmlhint --config .htmlhintrc.json *.html
       - run: sass-lint --config assets/css/.sass-lint.yml --verbose --no-exit --max-warnings 0
       - run: flake8 --config tools/.flake8.ini *.py **/**.py **/**/*.py
+      - run: flow check
 
       # Build project
       - run: cp config.conf.example config.conf
diff --git a/.flowconfig b/.flowconfig
index 28eb81569..d5f5265f9 100644
--- a/.flowconfig
+++ b/.flowconfig
@@ -1,5 +1,5 @@
 [ignore]
-build/
+.*/build/.*
 
 [include]
 
diff --git a/Makefile b/Makefile
index 59be3f5dc..e7e14a43c 100644
--- a/Makefile
+++ b/Makefile
@@ -5,7 +5,7 @@ debug: debugjs debugcss build/index.debug.html build/not-found.html fonts build/
 prod: js css html fonts build/sitemap.xml build/manifest.json build/strings/locales.json localhtml images
 
 js: build/js/min.js build/js/compat.js build/js/jquery.min.js build/js/bootstrap.min.js debugjs
-debugjs: build/js/jquery.jsonp-2.4.0.min.js build/js/config.js build/js/util.js build/js/store.js build/js/persistence.js build/js/localization.js build/js/translator.js build/js/analyzer.js build/js/generator.js build/js/sandbox.js
+debugjs: build/js/jquery.jsonp-2.4.0.min.js build/js/config.js build/js/util.js build/js/init.js build/js/store.js build/js/persistence.js build/js/localization.js build/js/translator.js build/js/analyzer.js build/js/generator.js build/js/sandbox.js
 css: build/css/min.css build/css/font-awesome.min.css build/css/bootstrap-rtl.min.css debugcss
 debugcss: build/css/bootstrap.css build/css/style.css
 html: build/index.html build/index.debug.html build/not-found.html
@@ -37,6 +37,7 @@ JSFILES= \
 	build/js/locales.js \
 	build/js/listrequests.js \
 	assets/js/util.js \
+	assets/js/init.js \
 	assets/js/store.js \
 	assets/js/persistence.js \
 	assets/js/localization.js \
@@ -226,10 +227,6 @@ build/img/%: assets/img/%
 
 images: $(IMAGES_BUILD)
 
-### Typechecking ###
-# grab the bin from https://github.com/facebook/flow/releases
-flow: build/js/all.js
-	grep -Ev '/\*:: *(ex|im)port ' $< | flow check-contents
 
 ### Test server ###
 server:
@@ -240,4 +237,4 @@ server:
 ### Clean ###
 clean:
 	rm -rf build/
-    
\ No newline at end of file
+
diff --git a/assets/js/analyzer.js b/assets/js/analyzer.js
index 0542eb711..3efe268fa 100644
--- a/assets/js/analyzer.js
+++ b/assets/js/analyzer.js
@@ -240,3 +240,9 @@ function formatUnit(unit) {
 function handleAnalyzeErrorResponse(xOptions, error) {
     $('#morphAnalyzerOutput').text(error).removeClass('blurred');
 }
+
+/*:: import {config} from "./config.js" */
+/*:: import {modeEnabled, ajaxSend, ajaxComplete, filterLangList, allowedLang, sendEvent, callApy, apyRequestTimeout} from "./util.js" */
+/*:: import {ENTER_KEY_CODE} from "./util.js" */
+/*:: import {localizeInterface, getLangByCode} from "./localization.js" */
+/*:: import {persistChoices, restoreChoices, readCache, cache} from "./persistence.js" */
diff --git a/assets/js/init.js b/assets/js/init.js
new file mode 100644
index 000000000..6cb0ab129
--- /dev/null
+++ b/assets/js/init.js
@@ -0,0 +1,181 @@
+/* global config, persistChoices, iso639Codes, iso639CodesInverse, populateTranslationList, showTranslateWebpageInterface */
+/* global ajaxSend, ajaxComplete, debounce, resizeFooter, synchronizeTextareaHeights */
+
+var BACK_TO_TOP_BUTTON_ACTIVATION_HEIGHT = 300;
+
+$(document).ajaxSend(ajaxSend);
+$(document).ajaxComplete(ajaxComplete);
+$(document).ajaxError(ajaxComplete);
+
+$.jsonp.setup({
+    callbackParameter: 'callback'
+});
+
+$(document).ready(function () {
+    $('#noscript').hide();
+    $('.navbar').css('margin-top', '0px');
+    $('body > .container').css('margin-top', '0px');
+
+    if(config.SUBTITLE) {
+        $('.apertiumSubLogo')
+            .text(config.SUBTITLE)
+            .show();
+        if(config.SUBTITLE_COLOR) {
+            $('.apertiumSubLogo').css('color', config.SUBTITLE_COLOR);
+        }
+    }
+    else {
+        $('.apertiumSubLogo').hide();
+    }
+
+    if(config.SHOW_NAVBAR) {
+        if(config.ENABLED_MODES === null) {
+            $('.nav a').removeClass('hide');
+        }
+        else {
+            $.each(config.ENABLED_MODES, function () {
+                $('.nav a[data-mode=' + this + ']').removeClass('hide');
+            });
+        }
+    }
+    else {
+        $('.navbar-default .navbar-toggle').hide();
+        $('.navbar-default .nav').hide();
+    }
+
+    var hash = parent.location.hash;
+
+    try {
+        if(!hash || !$(hash + 'Container')) {
+            hash = '#' + config.DEFAULT_MODE;
+            parent.location.hash = hash;
+        }
+    }
+    catch(e) {
+        console.error('Invalid hash: ' + e);
+        hash = '#' + config.DEFAULT_MODE;
+        parent.location.hash = hash;
+    }
+
+    try {
+        if(hash === '#webpageTranslation') {
+            hash = '#translation';
+            showTranslateWebpageInterface();
+        }
+        else if(!hash || !$(hash + 'Container').length) {
+            hash = '#' + config.DEFAULT_MODE;
+            parent.location.hash = hash;
+        }
+    }
+    catch(e) {
+        console.error('Invalid hash: ' + e);
+        hash = '#' + config.DEFAULT_MODE;
+        parent.location.hash = hash;
+    }
+
+    $('.modeContainer' + hash + 'Container').show();
+    $('.navbar-default .nav li > a[data-mode=' + hash.substring(1) + ']').parent().addClass('active');
+
+    $('.navbar-default .nav a').click(function () {
+        var mode = $(this).data('mode');
+        $('.nav li').removeClass('active');
+        $(this).parent('li').addClass('active');
+        $('.modeContainer:not(#' + mode + 'Container)').stop().hide({
+            queue: false
+        });
+        $('#' + mode + 'Container').stop().show({
+            queue: false
+        });
+        synchronizeTextareaHeights();
+    });
+
+    resizeFooter();
+    $(window)
+        .on('hashchange', persistChoices)
+        .resize(debounce(function () {
+            populateTranslationList();
+            resizeFooter();
+        }));
+
+    if(config.ALLOWED_LANGS) {
+        var withIso = [];
+        $.each(config.ALLOWED_LANGS, function () {
+            if(iso639Codes[this]) {
+                withIso.push(iso639Codes[this]);
+            }
+            if(iso639CodesInverse[this]) {
+                withIso.push(iso639CodesInverse[this]);
+            }
+        });
+        Array.prototype.push.apply(config.ALLOWED_LANGS, withIso);
+    }
+
+    $('form').submit(function () {
+        return false;
+    });
+
+    $('.modal').on('show.bs.modal', function () {
+        $('a[data-target=#' + $(this).attr('id') + ']').parents('li').addClass('active');
+        $.each($(this).find('img[data-src]'), function () {
+            $(this).attr('src', $(this).attr('data-src'));
+        });
+    });
+
+    $('.modal').on('hide.bs.modal', function () {
+        $('a[data-target=#' + $(this).attr('id') + ']').parents('li').removeClass('active');
+    });
+
+    $('#backToTop').addClass('hide');
+    $(window).scroll(function () {
+        $('#backToTop').toggleClass('hide', $(window).scrollTop() < BACK_TO_TOP_BUTTON_ACTIVATION_HEIGHT);
+    });
+
+    $('#backToTop').click(function () {
+        $('html, body').animate({
+            scrollTop: 0
+        }, 'fast');
+        return false;
+    });
+
+    $('#installationNotice').addClass('hide');
+});
+
+if(config.PIWIK_SITEID && config.PIWIK_URL) {
+    var url = config.PIWIK_URL;
+    if(document.location.protocol === 'https:') {
+        url = url.replace(/^(http(s)?)?:/, 'https:');
+    }
+    // but if we're on plain http, we keep whatever was in the config
+    if(url.charAt(url.length - 1) !== '/') {
+        url += '/';
+    }
+
+    /* eslint-disable */
+    var _paq = _paq || [];
+    _paq.push(['trackPageView']);
+    _paq.push(['enableLinkTracking']);
+    (function() {
+        var u=url;
+        _paq = _paq || [];
+        _paq.push(['setTrackerUrl', u+'piwik.php']);
+        _paq.push(['setSiteId', config.PIWIK_SITEID]);
+        var d=document,
+            g=d.createElement('script'),
+            s=d.getElementsByTagName('script')[0];
+        g.type='text/javascript';
+        g.defer=true;
+        g.async=true;
+        g.src=u+'piwik.js';
+        if(s.parentNode) {
+            s.parentNode.insertBefore(g,s);
+        }
+    })();
+    /* eslint-enable */
+}
+
+/*:: export {_paq} */
+/*:: import {config} from "./config.js" */
+/*:: import {persistChoices} from "./persistence.js" */
+/*:: import {iso639Codes, iso639CodesInverse} from "./localization.js" */
+/*:: import {populateTranslationList, showTranslateWebpageInterface} from "./translator.js" */
+/*:: import {ajaxSend, ajaxComplete, debounce, resizeFooter, synchronizeTextareaHeights} from "./util.js" */
diff --git a/assets/js/translator.js b/assets/js/translator.js
index d137f30f7..d15087b2e 100644
--- a/assets/js/translator.js
+++ b/assets/js/translator.js
@@ -24,7 +24,7 @@ var PUNCTUATION_KEY_CODES = [46, 33, 58, 63, 47, 45, 190, 171, 49]; // eslint-di
 /* global config, modeEnabled, synchronizeTextareaHeights, persistChoices, getLangByCode, sendEvent, onlyUnique, restoreChoices
     getDynamicLocalization, locale, ajaxSend, ajaxComplete, localizeInterface, filterLangList, cache, readCache, iso639Codes,
     callApy, apyRequestTimeout, isURL */
-/* global SPACE_KEY_CODE, ENTER_KEY_CODE, HTTP_OK_CODE, XHR_LOADING, XHR_DONE, HTTP_OK_CODE, HTTP_BAD_REQUEST_CODE */
+/* global SPACE_KEY_CODE, ENTER_KEY_CODE, HTTP_OK_CODE, XHR_LOADING, XHR_DONE, HTTP_BAD_REQUEST_CODE */
 
 if(modeEnabled('translation')) {
     $(document).ready(function () {
@@ -1074,10 +1074,11 @@ function autoSelectDstLang() {
     }
 }
 
-/*:: import {synchronizeTextareaHeights, modeEnabled, ajaxSend, ajaxComplete, filterLangList, onlyUnique, getLangByCode,
-    callApy, apyRequestTimeout} from "./util.js" */
+/*:: export {populateTranslationList, showTranslateWebpageInterface} */
+/*:: import {synchronizeTextareaHeights, modeEnabled, ajaxSend, ajaxComplete, filterLangList, onlyUnique, sendEvent, callApy,
+    apyRequestTimeout, SPACE_KEY_CODE, ENTER_KEY_CODE, HTTP_OK_CODE, XHR_LOADING, XHR_DONE, HTTP_BAD_REQUEST_CODE} from "./util.js" */
 /*:: import {persistChoices, restoreChoices} from "./persistence.js" */
-/*:: import localizeInterface from "./localization.js" */
-/*:: import {readCache,cache} from "./cache.js" */
+/*:: import {localizeInterface, getLangByCode, getDynamicLocalization, locale, iso639Codes} from "./localization.js" */
+/*:: import {readCache, cache} from "./persistence.js" */
 /*:: import {config} from "./config.js" */
 /*:: import {isURL} from "./util.js" */
diff --git a/assets/js/util.js b/assets/js/util.js
index af135608f..602da80a6 100644
--- a/assets/js/util.js
+++ b/assets/js/util.js
@@ -1,14 +1,14 @@
 /* @flow */
-/* exported sendEvent, modeEnabled, filterLangList, getURLParam, onlyUnique, isSubset, safeRetrieve, callApy, apyRequestTimeout, isURL */
+/* exported debounce, ajaxComplete, sendEvent, modeEnabled, resizeFooter, filterLangList, getURLParam, onlyUnique, isSubset */
+/* exported synchronizeTextareaHeights, callApy, apyRequestTimeout, isURL */
 /* exported SPACE_KEY_CODE, ENTER_KEY_CODE, HTTP_OK_CODE, HTTP_BAD_REQUEST_CODE, XHR_LOADING, XHR_DONE */
-/* global config, persistChoices, iso639Codes, iso639CodesInverse, populateTranslationList, showTranslateWebpageInterface */
+/* global _paq, config */
 
 var SPACE_KEY_CODE = 32, ENTER_KEY_CODE = 13,
     HTTP_OK_CODE = 200, HTTP_BAD_REQUEST_CODE = 400,
     XHR_LOADING = 3, XHR_DONE = 4;
 
 var TEXTAREA_AUTO_RESIZE_MINIMUM_WIDTH = 768,
-    BACK_TO_TOP_BUTTON_ACTIVATION_HEIGHT = 300,
     APY_REQUEST_URL_THRESHOLD_LENGTH = 2000, // maintain 48 characters buffer for generated parameters
     DEFAULT_DEBOUNCE_DELAY = 100;
 
@@ -71,176 +71,6 @@ function ajaxComplete() {
     }
 }
 
-$(document).ajaxSend(ajaxSend);
-$(document).ajaxComplete(ajaxComplete);
-$(document).ajaxError(ajaxComplete);
-
-$.jsonp.setup({
-    callbackParameter: 'callback'
-});
-
-$(document).ready(function () {
-    $('#noscript').hide();
-    $('.navbar').css('margin-top', '0px');
-    $('body > .container').css('margin-top', '0px');
-
-    if(config.SUBTITLE) {
-        $('.apertiumSubLogo')
-            .text(config.SUBTITLE)
-            .show();
-        if(config.SUBTITLE_COLOR) {
-            $('.apertiumSubLogo').css('color', config.SUBTITLE_COLOR);
-        }
-    }
-    else {
-        $('.apertiumSubLogo').hide();
-    }
-
-    if(config.SHOW_NAVBAR) {
-        if(config.ENABLED_MODES === null) {
-            $('.nav a').removeClass('hide');
-        }
-        else {
-            $.each(config.ENABLED_MODES, function () {
-                $('.nav a[data-mode=' + this + ']').removeClass('hide');
-            });
-        }
-    }
-    else {
-        $('.navbar-default .navbar-toggle').hide();
-        $('.navbar-default .nav').hide();
-    }
-
-    var hash = parent.location.hash;
-
-    try {
-        if(!hash || !$(hash + 'Container')) {
-            hash = '#' + config.DEFAULT_MODE;
-            parent.location.hash = hash;
-        }
-    }
-    catch(e) {
-        console.error('Invalid hash: ' + e);
-        hash = '#' + config.DEFAULT_MODE;
-        parent.location.hash = hash;
-    }
-
-    try {
-        if(hash === '#webpageTranslation') {
-            hash = '#translation';
-            showTranslateWebpageInterface();
-        }
-        else if(!hash || !$(hash + 'Container').length) {
-            hash = '#' + config.DEFAULT_MODE;
-            parent.location.hash = hash;
-        }
-    }
-    catch(e) {
-        console.error('Invalid hash: ' + e);
-        hash = '#' + config.DEFAULT_MODE;
-        parent.location.hash = hash;
-    }
-
-    $('.modeContainer' + hash + 'Container').show();
-    $('.navbar-default .nav li > a[data-mode=' + hash.substring(1) + ']').parent().addClass('active');
-
-    $('.navbar-default .nav a').click(function () {
-        var mode = $(this).data('mode');
-        $('.nav li').removeClass('active');
-        $(this).parent('li').addClass('active');
-        $('.modeContainer:not(#' + mode + 'Container)').stop().hide({
-            queue: false
-        });
-        $('#' + mode + 'Container').stop().show({
-            queue: false
-        });
-        synchronizeTextareaHeights();
-    });
-
-    resizeFooter();
-    $(window)
-        .on('hashchange', persistChoices)
-        .resize(debounce(function () {
-            populateTranslationList();
-            resizeFooter();
-        }));
-
-    if(config.ALLOWED_LANGS) {
-        var withIso = [];
-        $.each(config.ALLOWED_LANGS, function () {
-            if(iso639Codes[this]) {
-                withIso.push(iso639Codes[this]);
-            }
-            if(iso639CodesInverse[this]) {
-                withIso.push(iso639CodesInverse[this]);
-            }
-        });
-        Array.prototype.push.apply(config.ALLOWED_LANGS, withIso);
-    }
-
-    $('form').submit(function () {
-        return false;
-    });
-
-    $('.modal').on('show.bs.modal', function () {
-        $('a[data-target=#' + $(this).attr('id') + ']').parents('li').addClass('active');
-        $.each($(this).find('img[data-src]'), function () {
-            $(this).attr('src', $(this).attr('data-src'));
-        });
-    });
-
-    $('.modal').on('hide.bs.modal', function () {
-        $('a[data-target=#' + $(this).attr('id') + ']').parents('li').removeClass('active');
-    });
-
-    $('#backToTop').addClass('hide');
-    $(window).scroll(function () {
-        $('#backToTop').toggleClass('hide', $(window).scrollTop() < BACK_TO_TOP_BUTTON_ACTIVATION_HEIGHT);
-    });
-
-    $('#backToTop').click(function () {
-        $('html, body').animate({
-            scrollTop: 0
-        }, 'fast');
-        return false;
-    });
-
-    $('#installationNotice').addClass('hide');
-});
-
-if(config.PIWIK_SITEID && config.PIWIK_URL) {
-    var url = config.PIWIK_URL;
-    if(document.location.protocol === 'https:') {
-        url = url.replace(/^(http(s)?)?:/, 'https:');
-    }
-    // but if we're on plain http, we keep whatever was in the config
-    if(url.charAt(url.length - 1) !== '/') {
-        url += '/';
-    }
-
-    /* eslint-disable */
-    var _paq = _paq || [];
-    _paq.push(['trackPageView']);
-    _paq.push(['enableLinkTracking']);
-    (function() {
-        var u=url;
-        _paq = _paq || [];
-        _paq.push(['setTrackerUrl', u+'piwik.php']);
-        _paq.push(['setSiteId', config.PIWIK_SITEID]);
-        var d=document,
-            g=d.createElement('script'),
-            s=d.getElementsByTagName('script')[0];
-        g.type='text/javascript';
-        g.defer=true;
-        g.async=true;
-        g.src=u+'piwik.js';
-        if(s.parentNode) {
-            s.parentNode.insertBefore(g,s);
-        }
-    })();
-    /* eslint-enable */
-}
-
 /* eslint-disable id-blacklist */
 function sendEvent(category, action, label, value) {
     if(config.PIWIK_SITEID && config.PIWIK_URL && _paq) {
@@ -407,9 +237,7 @@ function displayInstallationNotification() {
     }
 }
 
-/*:: export {synchronizeTextareaHeights, modeEnabled, ajaxSend, ajaxComplete, filterLangList, onlyUnique, callApy,
-    SPACE_KEY_CODE, ENTER_KEY_CODE, HTTP_OK_CODE, HTTP_BAD_REQUEST_CODE, XHR_LOADING, XHR_DONE, apyRequestTimeout} */
+/*:: export {debounce, synchronizeTextareaHeights, modeEnabled, resizeFooter, ajaxSend, ajaxComplete, filterLangList, onlyUnique, callApy,
+    SPACE_KEY_CODE, ENTER_KEY_CODE, HTTP_OK_CODE, HTTP_BAD_REQUEST_CODE, XHR_LOADING, XHR_DONE, apyRequestTimeout, isURL, sendEvent} */
+/*:: import {_paq} from "./init.js" */
 /*:: import {config} from "./config.js" */
-/*:: import {persistChoices} from "./persistence.js" */
-/*:: import {iso639Codes, iso639CodesInverse} from "./localization.js" */
-/*:: import {populateTranslationList, showTranslateWebpageInterface} from "./translator.js" */
diff --git a/debug-head.html b/debug-head.html
index 324e970df..fa3a4668c 100644
--- a/debug-head.html
+++ b/debug-head.html
@@ -3,6 +3,7 @@
         <script type="text/javascript" src="./js/jquery.jsonp-2.4.0.min.js"></script>
         <script type="text/javascript" src="./js/config.js"></script>
         <script type="text/javascript" src="./js/util.js"></script>
+        <script type="text/javascript" src="./js/init.js"></script>
         <script type="text/javascript" src="./js/store.js"></script>
         <script type="text/javascript" src="./js/persistence.js"></script>
         <script type="text/javascript" src="./js/localization.js"></script>