diff --git a/eslint/eslintrc.json b/eslint/eslintrc.json
index 92436b8..77aaba5 100644
--- a/eslint/eslintrc.json
+++ b/eslint/eslintrc.json
@@ -33,6 +33,7 @@
         "quote-props": ["warn", "as-needed"],
         "no-unused-vars": ["error", {"argsIgnorePattern": "^_"}],
         "max-len" : ["warn", {"code": 88}],
-        "capitalized-comments": "off"
+        "capitalized-comments": "off",
+        "operator-linebreak": ["warn", "before"]
     }
 }
diff --git a/melpomene.js b/melpomene.js
index 4ad7a55..8572c8c 100644
--- a/melpomene.js
+++ b/melpomene.js
@@ -91,11 +91,11 @@ function pageMaxHeight()
 {
     let maxHeight = 0;
 
-    for (let i = 0; i < READER_PAGES.children.length; i += 1)
+    for (let pageIdx = 0; pageIdx < READER_PAGES.children.length; pageIdx += 1)
     {
-        if(READER_PAGES.children[i].naturalHeight > maxHeight)
+        if (READER_PAGES.children[pageIdx].naturalHeight > maxHeight)
         {
-            maxHeight = READER_PAGES.children[i].naturalHeight;
+            maxHeight = READER_PAGES.children[pageIdx].naturalHeight;
         }
     }
 
@@ -104,7 +104,7 @@ function pageMaxHeight()
 
 function pageVerticalOffset(pageNumber)
 {
-    return ( pageMaxHeight() - pageOriginalHeight(pageNumber) ) / 2;
+    return (pageMaxHeight() - pageOriginalHeight(pageNumber)) / 2;
 }
 
 function previousPagesWidth(pageNumber)
@@ -169,9 +169,9 @@ function loadZoomsFromImgTagsIfRequired()
             // ";" separates zooms data, "," separates values
             // We add the page number (adding 1 because of indexing)
             const zooms = zoomsRawData.split(";").map(
-                zoom => [idx + 1].concat(
+                (zoom) => [idx + 1].concat(
                     zoom.split(",").map(
-                        value => parseFloat(value)
+                        (value) => parseFloat(value)
                     )
                 )
             );
@@ -190,16 +190,18 @@ function getFirstZoomOfPage(pageNumber)
             return zoomIdx;
         }
     }
+
+    return undefined;
 }
 
 function getZoomCountForPage(pageNumber)
 {
-    return PAGES_ZOOMS.filter(zoom => zoom[0] === pageNumber).length;
+    return PAGES_ZOOMS.filter((zoom) => zoom[0] === pageNumber).length;
 }
 
 function getCurrentZoomIndexForPage()
 {
-    const previousZoomsCount = PAGES_ZOOMS.filter(zoom => zoom[0] < CURRENT_PAGE).length;
+    const previousZoomsCount = PAGES_ZOOMS.filter((zoom) => zoom[0] < CURRENT_PAGE).length;
     return CURRENT_ZOOM - previousZoomsCount + 1;
 }
 
@@ -214,14 +216,16 @@ function getReadingProgressPercent()
 
     const progressPerZoom = progressPerPage / getZoomCountForPage(CURRENT_PAGE);
 
-    const readingProgress = (CURRENT_PAGE - 1) * progressPerPage + getCurrentZoomIndexForPage() * progressPerZoom;
+
+    let readingProgress = (CURRENT_PAGE - 1) * progressPerPage;
+    readingProgress += getCurrentZoomIndexForPage() * progressPerZoom;
 
     return 100 * readingProgress;
 }
 
 function updateProgressBar()
 {
-    PROGRESS_BAR.style.width = getReadingProgressPercent() + "%";
+    PROGRESS_BAR.style.width = `${getReadingProgressPercent()}%`;
 }
 
 // =========
@@ -265,7 +269,7 @@ function moveReaderDisplayToArea(pageNumber, oWidth, oHeight, oPosx, oPosy)
         posx = 0;
     }
 
-    if ((posx + width) > pageOriginalWidth(pageNumber))
+    if (posx + width > pageOriginalWidth(pageNumber))
     {
         width = pageOriginalWidth(pageNumber) - posx;
     }
@@ -277,7 +281,7 @@ function moveReaderDisplayToArea(pageNumber, oWidth, oHeight, oPosx, oPosy)
         posy = 0;
     }
 
-    if ((posy + height) > pageOriginalHeight(pageNumber))
+    if (posy + height > pageOriginalHeight(pageNumber))
     {
         height = pageOriginalHeight(pageNumber) - posy;
     }
@@ -342,7 +346,13 @@ function moveReaderDisplayToArea(pageNumber, oWidth, oHeight, oPosx, oPosy)
 
 function refreshReaderDisplay()
 {
-    moveReaderDisplayToArea(CURRENT_PAGE, CURRENT_WIDTH, CURRENT_HEIGHT, CURRENT_X, CURRENT_Y);
+    moveReaderDisplayToArea(
+        CURRENT_PAGE,
+        CURRENT_WIDTH,
+        CURRENT_HEIGHT,
+        CURRENT_X,
+        CURRENT_Y
+    );
 }
 
 function moveReaderDisplayToPage(pageNumber)
@@ -352,7 +362,13 @@ function moveReaderDisplayToPage(pageNumber)
 
 function moveReaderDisplayToZoom(index)
 {
-    moveReaderDisplayToArea(PAGES_ZOOMS[index][0], PAGES_ZOOMS[index][1], PAGES_ZOOMS[index][2], PAGES_ZOOMS[index][3], PAGES_ZOOMS[index][4]);
+    moveReaderDisplayToArea(
+        PAGES_ZOOMS[index][0],
+        PAGES_ZOOMS[index][1],
+        PAGES_ZOOMS[index][2],
+        PAGES_ZOOMS[index][3],
+        PAGES_ZOOMS[index][4]
+    );
 
     CURRENT_ZOOM = index;
 }
@@ -445,12 +461,15 @@ function initReader()
                 }
             });
         },
-        { root: READER_CONTENT_FRAME, rootMargin: "-10px" }
+        {
+            root: READER_CONTENT_FRAME,
+            rootMargin: "-10px"
+        }
     );
 
-    for (let i = 0; i < READER_PAGES.children.length; i += 1)
+    for (let pageIndex = 0; pageIndex < READER_PAGES.children.length; pageIndex += 1)
     {
-        const img = READER_PAGES.children[i];
+        const img = READER_PAGES.children[pageIndex];
         visibilityObserver.observe(img);
 
         PROGRESS_BAR_PAGES.appendChild(document.createElement("div"));
@@ -459,7 +478,7 @@ function initReader()
     READER_PAGES.style.display = "flex";
 
     setTimeout(
-        () => { READER_PAGES.hidden = false },
+        () => { READER_PAGES.hidden = false; },
         "300"
     );