diff --git a/manifest.json b/manifest.json
index 4e345b2..e6dad09 100755
--- a/manifest.json
+++ b/manifest.json
@@ -16,9 +16,10 @@
   },
   "background": {
     "scripts": [
+      "scripts/background.js",
+      "scripts/csv.js",
       "scripts/tools.js",
-      "scripts/extract.js",
-      "scripts/background.js"
+      "scripts/extract.js"
     ],
     "persistent": false
   },
@@ -26,7 +27,6 @@
     "matches": ["*://*/*"],
     "js": [
       "scripts/jquery.min.js",
-      "scripts/tools.js",
       "scripts/content.js"
     ],
     "run_at": "document_idle"
diff --git a/scripts/content.js b/scripts/content.js
index 10b432f..5a07bf5 100644
--- a/scripts/content.js
+++ b/scripts/content.js
@@ -79,12 +79,7 @@ function extract(...args) {
         console.log(sig);
         return;
     }
-    if (args.length == 2) {
-        let data = extractTabData(args[0], args[1]);
-        data.unshift(args[1]);
-        saveFileAsk(data);
-        return;
-    }
+
     let message = {
         from: "DataExtracter:Extract",
         args: args
diff --git a/scripts/csv.js b/scripts/csv.js
new file mode 100644
index 0000000..87a6ab0
--- /dev/null
+++ b/scripts/csv.js
@@ -0,0 +1,31 @@
+class CSV {
+    constructor(data) {
+        this._data = data || [];
+
+    }
+    row(index) {
+        return this._data[index];
+    }
+    column(index) {
+        return new [...Array(this._data.length).keys].map(
+            i => this._data[i, index]
+        );
+    }
+    get data() {
+        return this._data;
+    }
+    toString(rowsCount) {
+        let data = rowsCount > 0 ? this._data.slice(0, rowsCount) : this._data;
+        return data.slice().reduce(
+            (csv, lineCells) => {
+                let line = lineCells.reduce(
+                    (lineText, cell, idx) => {
+                        cell = '"' + cell.trim().replace(/"/g, '""') + '"';
+                        return lineText + cell + (idx == lineCells.length - 1 ? "" : ",")
+                    }, "");
+                return csv + line + "\n";
+            },
+            ""
+        );
+    }
+}
\ No newline at end of file
diff --git a/scripts/extract.js b/scripts/extract.js
index 6698a72..ff5bb14 100644
--- a/scripts/extract.js
+++ b/scripts/extract.js
@@ -5,9 +5,12 @@
  * @param {...any} args url list / url templates, page numers, either [from, to, interval] or [...pages]
  */
 async function extract(itemsSelector, fieldSelectors, ...args) {
-    let data = await getData(itemsSelector, fieldSelectors, ...args);
-    data.unshift(fieldSelectors);
-    saveFileAsk(data);
+    let result = await getData(itemsSelector, fieldSelectors, ...args);
+    if (confirm(
+            `Click confirm to download if the sample data looks good (${result.data.length} items)：\n\n${result.toString(50) || "- Empty -"}`
+        )) {
+        saveFile(result, "text/csv");
+    }
 }
 
 /**
@@ -18,53 +21,51 @@ async function extract(itemsSelector, fieldSelectors, ...args) {
  */
 async function getData(itemsSelector, fieldSelectors, ...args) {
     let urls = [];
-    let arg = args.shift();
-    if (arg instanceof Array) {
-        urls = arg;
-    } else {
-        let urlTempl = arg;
-        if (urlTempl) {
-            if (args[0] instanceof Array) {
-                urls = args[0].map(p => urlTempl.replace("${page}", p));
-            } else if (args.length >= 3) {
-                let from = args.shift();
-                let to = args.shift();
-                let interval = args.shift();
-                for (let i = from; i <= to; i += interval) {
-                    urls.push(urlTempl.replace("${page}", i));
+    if (args.length) {
+        let arg = args.shift();
+        if (arg instanceof Array) {
+            urls = arg;
+        } else {
+            let urlTempl = arg;
+            if (urlTempl) {
+                if (args[0] instanceof Array) {
+                    urls = args[0].map(p => urlTempl.replace("${page}", p));
+                } else if (args.length >= 3) {
+                    let from = args.shift();
+                    let to = args.shift();
+                    let interval = args.shift();
+                    for (let i = from; i <= to; i += interval) {
+                        urls.push(urlTempl.replace("${page}", i));
+                    }
                 }
             }
         }
     }
     let data = [];
+    let tab = await getActiveTab(true) || await getActiveTab(false);
+    if (!tab) throw new Error("Cannot find active tab.");
     return new Promise((resolve, reject) => {
-        chrome.tabs.query({
-            active: true,
-            currentWindow: false
-        }, function (tabs) {
-            let pms;
-            let tab = tabs[0];
-            if (urls.length) {
-                pms = urls.reduce((p, url) => p.then(
-                    results => {
-                        data.push(...results);
-                        return redirectTab(tab, url).then(
-                            () => extractTabData(tab, itemsSelector, fieldSelectors)
-                        );
-                    },
-                    () => p
-                ), Promise.resolve([]));
-            } else {
-                pms = extractTabData(tab, itemsSelector, fieldSelectors);
-            }
-            pms.then(
+        let pms;
+        if (urls.length) {
+            pms = urls.reduce((p, url) => p.then(
                 results => {
                     data.push(...results);
-                    resolve(data);
+                    return redirectTab(tab, url).then(
+                        () => extractTabData(tab, itemsSelector, fieldSelectors)
+                    );
                 },
-                err => reject(err)
-            );
-        });
+                () => p
+            ), Promise.resolve([]));
+        } else {
+            pms = extractTabData(tab, itemsSelector, fieldSelectors);
+        }
+        pms.then(
+            results => {
+                data.push(...results);
+                resolve(new CSV(data));
+            },
+            err => reject(err)
+        );
     });
 }
 
@@ -163,4 +164,15 @@ function sendMessage(tab, req, cond, failedTimeOut, detectInterval) {
             });
         }
     });
+}
+
+async function getActiveTab(currentWindow) {
+    return new Promise((resolve, reject) => {
+        chrome.tabs.query({
+            active: true,
+            currentWindow: currentWindow
+        }, function (tabs) {
+            resolve(tabs[0]);
+        })
+    })
 }
\ No newline at end of file
diff --git a/scripts/tools.js b/scripts/tools.js
index ee39187..9eadea2 100644
--- a/scripts/tools.js
+++ b/scripts/tools.js
@@ -1,17 +1,3 @@
-function formatCSV(data) {
-    return data.reduce(
-        (csv, lineCells) => {
-            let line = lineCells.reduce(
-                (lineText, cell, idx) => {
-                    cell = '"' + cell.trim().replace(/"/g, '""') + '"';
-                    return lineText + cell + (idx == lineCells.length - 1 ? "" : ",")
-                }, "");
-            return csv + line + "\n";
-        },
-        ""
-    );
-}
-
 function saveFile(data, mimeType, fileName) {
     fileName = fileName || document.title || "result";
     var blob;
@@ -42,12 +28,4 @@ function saveFile(data, mimeType, fileName) {
     } else {
         location.href = url
     }
-}
-
-function saveFileAsk(data) {
-    let csv = formatCSV(data.slice(1, 50)).trim() || "- Empty -";
-    if (confirm(`Click confirm to download if the sample data looks good (${data.length-1} items)：\n\n${csv}`)) {
-        csv = formatCSV(data);
-        saveFile(csv, "text/csv");
-    }
 }
\ No newline at end of file