diff --git a/README.md b/README.md
index e3e96c2..296a1ac 100644
--- a/README.md
+++ b/README.md
@@ -118,10 +118,11 @@ Place `<%= image[IMG_ID] %>` inside the chapter's content *(HTML string only)*,
 ### Generate EPUB `*`
 
 ```typescript
-jepub.generate(type = 'blob')
+jepub.generate(type = 'blob', onUpdate?: metadata => void)
 ```
 
 - **type**: The type of EPUB to return. See [JSZip type option](https://stuk.github.io/jszip/documentation/api_jszip/generate_async.html#type-option).
+- **onUpdate**: _(optional)_ Callback function. See [JSZip onUpdate callback](https://stuk.github.io/jszip/documentation/api_jszip/generate_async.html#onupdate-callback).
 
 ### Static methods `+`
 
diff --git a/demo/script.js b/demo/script.js
index c9fb1d6..7bc3806 100644
--- a/demo/script.js
+++ b/demo/script.js
@@ -42,7 +42,10 @@
     ]);
 
     console.log(jepub);
-    const blob = await jepub.generate();
+    const blob = await jepub.generate('blob', metadata => {
+        console.log('progression: ' + metadata.percent.toFixed(2) + ' %');
+        if (metadata.currentFile) console.log('current file = ' + metadata.currentFile);
+    });
     console.log(blob);
 
     let url = URL.createObjectURL(blob);
diff --git a/src/jepub.js b/src/jepub.js
index 31aa75a..06113f2 100644
--- a/src/jepub.js
+++ b/src/jepub.js
@@ -188,7 +188,7 @@ export default class jEpub {
         }
     }
 
-    generate(type = 'blob') {
+    generate(type = 'blob', onUpdate) {
         if (!JSZip.support[type]) throw `This browser does not support ${type}`;
 
         let notes = this._Zip.file('OEBPS/notes.html');
@@ -236,6 +236,6 @@ export default class jEpub {
             compressionOptions: {
                 level: 9
             }
-        });
+        }, onUpdate);
     }
 }