diff --git a/hot-reload.js b/hot-reload.js
index de5e58c..f0865da 100644
--- a/hot-reload.js
+++ b/hot-reload.js
@@ -1,3 +1,5 @@
+const includes = []
+
 const filesInDirectory = dir => new Promise (resolve =>
 
     dir.createReader ().readEntries (entries =>
@@ -13,9 +15,15 @@ const filesInDirectory = dir => new Promise (resolve =>
     )
 )
 
-const timestampForFilesInDirectory = dir =>
-        filesInDirectory (dir).then (files =>
-            files.map (f => f.name + f.lastModifiedDate).join ())
+const timestampForFilesInDirectory = dir => {
+        return filesInDirectory (dir).then (files => {
+            if (includes.length && !includes.every(i => files.some(f => i === f.name))) return;
+
+            return files
+                .filter(f => includes.length ? includes.includes(f.name) : true)
+                .map (f => f.name + f.lastModifiedDate).join ()
+        })
+}
 
 const reload = () => {
 
@@ -31,7 +39,7 @@ const watchChanges = (dir, lastTimestamp) => {
 
     timestampForFilesInDirectory (dir).then (timestamp => {
 
-        if (!lastTimestamp || (lastTimestamp === timestamp)) {
+        if (!timestamp || !lastTimestamp || (lastTimestamp === timestamp)) {
 
             setTimeout (() => watchChanges (dir, timestamp), 1000) // retry after 1s
 
@@ -50,3 +58,10 @@ chrome.management.getSelf (self => {
         chrome.runtime.getPackageDirectoryEntry (dir => watchChanges (dir))
     }
 })
+
+if (typeof module === 'object') {
+    exports.include = (files) => {
+        includes.push(...files)
+    }
+}
+