Addressed comments.

functions/index.js

@@ -7,7 +7,10 @@ const jwt = require('jsonwebtoken');
 const fs = require('fs');
 
 /**
- * Data and images handling for Screenshot test
+ * Data and images handling for Screenshot test.
+ *
+ * All users can post data to temporary folder. These Functions will check the data with JsonWebToken and
+ * move the valid data out of temporary folder.
  *
  * For valid data posted to database /$temp/screenshot/reports/$prNumber/$secureToken, move it to
  * /screenshot/reports/$prNumber.
@@ -87,6 +90,7 @@ exports.copyImage = firebaseFunctions.database.ref(copyImagePath).onWrite(event
     const binaryData = new Buffer(event.data.val(), 'base64').toString('binary');
     fs.writeFile(tempPath, binaryData, 'binary');
     return bucket.upload(tempPath, {destination: filePath}).then(() => {
+      // Clear the data in temporary folder after processed.
       return event.data.ref.parent.set(null);
     });
   }).catch((error) => {
@@ -124,6 +128,10 @@ exports.copyGoldens = firebaseFunctions.storage.bucket(firebaseFunctions.config(
   });
 });
 
+/**
+ * Handle data written to temporary folder. Validate the JWT and move the data out of
+ * temporary folder if the token is valid.
+ */
 function handleDataChange(event, path) {
   // Only edit data when it is first created. Exit when the data is deleted.
   if (event.data.previous.exists() || !event.data.exists()) {
@@ -137,6 +145,7 @@ function handleDataChange(event, path) {
   return validateSecureToken(secureToken, prNumber).then((payload) => {
     return firebaseAdmin.database().ref().child('screenshot/reports')
         .child(prNumber).child(path).set(original).then(() => {
+      // Clear the data in temporary folder after processed.
       return event.data.ref.parent.set(null);
     });
   }).catch((error) => {

tools/gulp/tasks/screenshots.ts

@@ -120,13 +120,13 @@ function uploadScreenshotsData(database: firebase.database.Database,
                                mode: 'test' | 'diff', prNumber: string) {
   let localDir = mode == 'diff' ? path.join(SCREENSHOT_DIR, 'diff') : SCREENSHOT_DIR;
   let promises: any[] = [];
-  getLocalScreenshotFiles(localDir).forEach((file: string) => {
+  let promises = getLocalScreenshotFiles(localDir).map((file: string) => {
     let fileName = path.join(localDir, file);
     let filenameKey = extractScreenshotName(fileName);
     let secureToken = getSecureToken();
     let data = readFileSync(fileName);
-    promises.push(database.ref(FIREBASE_IMAGE).child(prNumber)
-      .child(secureToken).child(mode).child(filenameKey).set(data));
+    return database.ref(FIREBASE_IMAGE).child(prNumber)
+      .child(secureToken).child(mode).child(filenameKey).set(data);
   });
   return Promise.all(promises);
 }
@@ -195,17 +195,14 @@ function updateGithubStatus(prNumber: number, result: boolean) {
   });
 }
 
-/**
- * Upload screenshots to google cloud storage.
- */
+/** Upload screenshots to google cloud storage. */
 function uploadScreenshots() {
   let bucket = openScreenshotsBucket();
 
-  let promises: any[] = [];
-  getLocalScreenshotFiles(SCREENSHOT_DIR).forEach((file: string) => {
+  let promises = getLocalScreenshotFiles(SCREENSHOT_DIR).map((file: string) => {
     let fileName = path.join(SCREENSHOT_DIR, file);
     let destination = `golds/${file}`;
-    promises.push(bucket.upload(fileName, { destination: destination }));
+    return bucket.upload(fileName, { destination: destination });
   });
   return Promise.all(promises);
 }