scrollToBottom option

scripts/content/content.js

@@ -1,53 +1,101 @@
-chrome.runtime.onMessage.addListener(
-    function (request, sender, sendResponse) {
-        if (!request.action) return;
-        // console.log("Recieved request:",request);
+(function () {
+    chrome.runtime.onMessage.addListener(
+        function (request, sender, sendResponse) {
+            if (!request.action) return;
+            // console.log("Recieved request:",request);
+            doAction(request, sender).then(r => sendResponse && sendResponse(r));
+            // return true to indicate you wish to send a response asynchronously
+            return true;
+        }
+    );
+
+    async function doAction(request, sender) {
         switch (request.action) {
             case ACTION_EXTRACT:
                 let data = extract(request.itemsSelector, request.fieldSelectors);
-                if (sendResponse) sendResponse(data);
-                break;
+                return data;
             case ACTION_GOTO_URL:
                 window.location.replace(request.url);
-                if (sendResponse) sendResponse(request.url);
-                break;
+                return request.url;
             case ACTION_REPORT_IN:
-                if (sendResponse) sendResponse(request.action);
-                break;
+                return request.action;
             case ACTION_QUERY_URL:
-                if (sendResponse) sendResponse(window.location.href);
-                break;
+                return window.location.href;
+            case ACTION_SCROLL_BOTTOM:
+                return executeUntil(
+                    () => window.scrollTo(0, document.body.clientHeight),
+                    () => document.body.clientHeight - window.scrollY - window.innerHeight < 20,
+                    "Scroll to page bottom...",
+                    1000,
+                    10
+                )
             default:
                 break;
         }
     }
-);
 
-function extract(itemsSelector, fieldSelectors) {
-    // since some elements may be loaded asynchronously.
-    // if one field is never found, we should return undefined,
-    // so that senders can detect to retry until elements loaded.
-    // If user writes wrong selectors, the task retries infinitely.
-    let fieldFound = {};
-    let items = Array.from(document.querySelectorAll(itemsSelector));
-    // items may not loaded yet, tell the sender to retry.
-    if (!items.length) return MSG_ELEMENT_NOT_FOUND;
-    let results = items.map(
-        item => {
-            return fieldSelectors.map(
-                selector => {
-                    let [cls, attr] = selector.split('@').slice(0, 2);
-                    let fieldVals = Array.from(item.querySelectorAll(cls));
-                    if (!fieldVals.length) {
-                        return;
+    function extract(itemsSelector, fieldSelectors) {
+        // since some elements may be loaded asynchronously.
+        // if one field is never found, we should return undefined,
+        // so that senders can detect to retry until elements loaded.
+        // If user writes wrong selectors, the task retries infinitely.
+        let fieldFound = {};
+        let items = Array.from(document.querySelectorAll(itemsSelector));
+        // items may not loaded yet, tell the sender to retry.
+        if (!items.length) return MSG_ELEMENT_NOT_FOUND;
+        let results = items.map(
+            item => {
+                return fieldSelectors.map(
+                    selector => {
+                        let [cls, attr] = selector.split('@').slice(0, 2);
+                        let fieldVals = Array.from(item.querySelectorAll(cls));
+                        if (!fieldVals.length) {
+                            return;
+                        }
+                        fieldFound[selector] = true;
+                        return fieldVals.map(find => attr ? find[attr] : find.textContent.trim()).join('\n')
                     }
-                    fieldFound[selector] = true;
-                    return fieldVals.map(find => attr ? find[attr] : find.textContent.trim()).join('\n')
+                )
+            }
+        );
+        // if it exists a field, which is not found in any row, the sender should retry.
+        let shouldWait = fieldSelectors.reduce((p, c) => p || !fieldFound[c], false);
+        return shouldWait ? MSG_ELEMENT_NOT_FOUND : results
+    }
+
+    /**
+     * Repeatedly execute an function until the the detector returns true.
+     * @param {object} fn the function to execute
+     * @param {object} detector the detector.
+     * @param {string} log messages logged to console.
+     * @param {number} interval interval for detecting
+     * @param {number} limit max execute times of a function
+     * @return {Promise} a promise of the response.
+     */
+    function executeUntil(fn, detector, log, interval, limit) {
+        interval = interval || 500;
+        let count = 0;
+        return new Promise((resolve, reject) => {
+
+            loop();
+
+            async function loop() {
+                fn();
+                limit++;
+                if (limit && count >= limit) {
+                    reject(false);
                 }
-            )
-        }
-    );
-    // if it exists a field, which is not found in any row, the sender should retry.
-    let shouldWait = fieldSelectors.reduce((p, c) => p || !fieldFound[c], false);
-    return shouldWait ? MSG_ELEMENT_NOT_FOUND : results
-}
+                setTimeout(() => {
+                    let flag = !detector || detector();
+                    if (log) console.log(log, flag ? '(OK)' : '(failed)');
+                    if (flag) {
+                        resolve(true);
+                    } else {
+                        loop();
+                    }
+                }, interval);
+            }
+        });
+    }
+
+})();