Checking node object before checking its property.

chrome/browser/resources/bookmark_manager/js/bmm.js

Index: chrome/browser/resources/bookmark_manager/js/bmm.js
diff --git a/chrome/browser/resources/bookmark_manager/js/bmm.js b/chrome/browser/resources/bookmark_manager/js/bmm.js
index 8daf62cd720fded56fefc2f64486966d56809fc3..3c854aa6290aa44c0f61cdf3b66f31776dc3a01a 100644
--- a/chrome/browser/resources/bookmark_manager/js/bmm.js
+++ b/chrome/browser/resources/bookmark_manager/js/bmm.js
@@ -41,8 +41,14 @@ cr.define('bmm', function() {
    * @return {!Promise<!Array<!BookmarkTreeNode>>} .
    */
   function getSubtreePromise(id, foldersOnly) {
-    return new Promise(function(resolve) {
-      chrome.bookmarkManagerPrivate.getSubtree(id, foldersOnly, resolve);
+    return new Promise(function(resolve, reject) {
+      chrome.bookmarkManagerPrivate.getSubtree(id, foldersOnly, function(node) {
+        if (chrome.runtime.lastError) {
+          reject(new Error(chrome.runtime.lastError.message));
+          return;
+        }
+        resolve(node);
+      });
     });
   }
 
@@ -55,8 +61,16 @@ cr.define('bmm', function() {
   function loadSubtree(id) {
     if (!loadingPromises[id]) {
       loadingPromises[id] = getSubtreePromise(id, false).then(function(nodes) {
-        delete loadingPromises[id];
+        loadingPromises[id].then(function() {

[Bernhard Bauer, 2015/04/30 15:08:07]

You can pull this out into a single callback on loadingPromises[id] after you've
assigned a value to it. The reason why this works is that adding an error
handler will cause loadingPromises[id] to be a resolved promise, even if the
promise returned from getSubtreePromise is rejected. The error handler
effectively turns the rejected promise into a resolved one (with an undefined
value). Then the callback you add with .then is guaranteed to be called.

[Deepak, 2015/04/30 16:11:19]

Done.

+          delete loadingPromises[id];
+        });
         return nodes && nodes[0];
+      }, function(error) {
+        loadingPromises[id].then(function() {
+          delete loadingPromises[id];
+        });
+        console.error(error.message);
+        return;
       });
     }
     return loadingPromises[id];