diff --git a/src/js/vapi-common.js b/src/js/vapi-common.js
new file mode 100644
index 0000000..2997a11
--- /dev/null
+++ b/src/js/vapi-common.js
@@ -0,0 +1,62 @@
+// only for background and other extension pages
+/* global chrome, Components, BeforeLoadEvent */
+
+(function() {
+'use strict';
+
+window.vAPI = window.vAPI || {};
+
+if (window.chrome) {
+    var chrome = window.chrome;
+
+    vAPI.getURL = function(path) {
+        return chrome.runtime.getURL(path);
+    };
+
+    vAPI.i18n = function(s) {
+        return chrome.i18n.getMessage(s) || s;
+    };
+} else if (window.safari) {
+    vAPI.getURL = function(path) {
+        return safari.extension.baseURI + path;
+    };
+
+    var xhr = new XMLHttpRequest;
+    xhr.overrideMimeType('application/json;charset=utf-8');
+    xhr.open('GET', './locales.json', false);
+    xhr.send();
+    vAPI.i18nData = JSON.parse(xhr.responseText);
+
+    if (vAPI.i18nData[vAPI.i18n = navigator.language.replace('-', '_')]
+        || vAPI.i18nData[vAPI.i18n = vAPI.i18n.slice(0, 2)]) {
+        vAPI.i18nAlpha2 = vAPI.i18n;
+    } else {
+        vAPI.i18nAlpha2 = vAPI.i18nData._;
+    }
+
+    xhr = new XMLHttpRequest;
+    xhr.overrideMimeType('application/json;charset=utf-8');
+    xhr.open('GET', './_locales/' + vAPI.i18nAlpha2 + '/messages.json', false);
+    xhr.send();
+    vAPI.i18nData = JSON.parse(xhr.responseText);
+
+    for (var i18nKey in vAPI.i18nData) {
+        vAPI.i18nData[i18nKey] = vAPI.i18nData[i18nKey].message;
+    }
+
+    vAPI.i18n = function(s) {
+        return this.i18nData[s] || s;
+    };
+
+    // update popover size to its content
+    if (safari.self.identifier === 'popover' && safari.self) {
+        vAPI.updatePopoverSize = function() {
+            safari.self.width = document.body.clientWidth;
+            safari.self.height = document.body.clientHeight;
+        };
+
+        setTimeout(vAPI.updatePopoverSize, 200);
+    }
+}
+
+})();
\ No newline at end of file