diff --git a/.eslintrc.yml b/.eslintrc.yml
index 599d506aba..0c755d8b40 100644
--- a/.eslintrc.yml
+++ b/.eslintrc.yml
@@ -3,8 +3,8 @@ extends:
   - 'eslint:recommended'
   - 'plugin:node/recommended'
   - prettier
-env: 
-  mocha: true 
+env:
+  mocha: true
 plugins:
   - node
   - prettier
@@ -16,4 +16,4 @@ rules:
   no-console: off
   node/no-missing-require: off
   node/no-unpublished-require: off
-
+  prefer-const: error
diff --git a/appengine/headless-chrome/app.js b/appengine/headless-chrome/app.js
index 6d8a147cf6..a876fc09a6 100644
--- a/appengine/headless-chrome/app.js
+++ b/appengine/headless-chrome/app.js
@@ -39,7 +39,7 @@ app.use(async (req, res) => {
     // [END browser]
   }
 
-  let page = await browser.newPage();
+  const page = await browser.newPage();
   await page.goto(url);
   const imageBuffer = await page.screenshot();
 
diff --git a/appengine/memcached/app.js b/appengine/memcached/app.js
index e7dcb33d26..f854fd0c3c 100644
--- a/appengine/memcached/app.js
+++ b/appengine/memcached/app.js
@@ -22,7 +22,7 @@ const app = express();
 
 // [START gae_flex_redislabs_memcache]
 // Environment variables are defined in app.yaml.
-let MEMCACHE_URL = process.env.MEMCACHE_URL;
+const MEMCACHE_URL = process.env.MEMCACHE_URL;
 
 const mc = memjs.Client.create(MEMCACHE_URL);
 // [END gae_flex_redislabs_memcache]
diff --git a/appengine/metadata/standard/server.js b/appengine/metadata/standard/server.js
index 35b14ac9fa..10fb46346d 100644
--- a/appengine/metadata/standard/server.js
+++ b/appengine/metadata/standard/server.js
@@ -36,8 +36,8 @@ function getProjectId() {
 
 app.get('/', async (req, res, next) => {
   try {
-    let response = await getProjectId();
-    let projectId = response.body;
+    const response = await getProjectId();
+    const projectId = response.body;
     res
       .status(200)
       .send(`Project ID: ${projectId}`)
diff --git a/appengine/pubsub/app.js b/appengine/pubsub/app.js
index a76f0bf894..2a0efd553a 100644
--- a/appengine/pubsub/app.js
+++ b/appengine/pubsub/app.js
@@ -59,9 +59,9 @@ app.post('/', formBodyParser, async (req, res, next) => {
     return;
   }
 
-  let data = Buffer.from(req.body.payload);
+  const data = Buffer.from(req.body.payload);
   try {
-    let messageId = await publisher.publish(data);
+    const messageId = await publisher.publish(data);
     res.status(200).send(`Message ${messageId} sent.`);
   } catch (error) {
     next(error);
diff --git a/appengine/typescript/index.ts b/appengine/typescript/index.ts
index 0da7e3ee57..5660745a5a 100644
--- a/appengine/typescript/index.ts
+++ b/appengine/typescript/index.ts
@@ -21,6 +21,6 @@ app.get("/", (req, res) => {
   res.send("🎉 Hello TypeScript! 🎉");
 });
 
-const server: object = app.listen(PORT, () => {
+app.listen(PORT, () => {
   console.log(`App listening on port ${PORT}`);
 });
diff --git a/cloud-sql/postgres/knex/server.js b/cloud-sql/postgres/knex/server.js
index 52ec95fafd..d9ccbc55f8 100644
--- a/cloud-sql/postgres/knex/server.js
+++ b/cloud-sql/postgres/knex/server.js
@@ -152,13 +152,13 @@ async function getVoteCount(knex, candidate) {
 app.get('/', (req, res) => {
   (async function() {
     // Query the total count of "TABS" from the database.
-    let tabsResult = await getVoteCount(knex, 'TABS');
-    let tabsTotalVotes = parseInt(tabsResult[0].count);
+    const tabsResult = await getVoteCount(knex, 'TABS');
+    const tabsTotalVotes = parseInt(tabsResult[0].count);
     // Query the total count of "SPACES" from the database.
-    let spacesResult = await getVoteCount(knex, 'SPACES');
-    let spacesTotalVotes = parseInt(spacesResult[0].count);
+    const spacesResult = await getVoteCount(knex, 'SPACES');
+    const spacesTotalVotes = parseInt(spacesResult[0].count);
     // Query the last 5 votes from the database.
-    let votes = await getVotes(knex);
+    const votes = await getVotes(knex);
     // Calculate and set leader values.
     let leadTeam = '';
     let voteDiff = 0;
@@ -219,7 +219,7 @@ app.post('/', (req, res) => {
         .send(msg)
         .end();
     });
-  let msg = 'Successfully voted for ' + team + ' at ' + timestamp;
+  const msg = 'Successfully voted for ' + team + ' at ' + timestamp;
   res
     .status(200)
     .send(msg)
diff --git a/functions/http/index.js b/functions/http/index.js
index 38f3e9baae..79deb162da 100644
--- a/functions/http/index.js
+++ b/functions/http/index.js
@@ -99,8 +99,8 @@ exports.helloHttp = (req, res) => {
 exports.parseXML = (req, res) => {
   // Convert the request to a Buffer and a string
   // Use whichever one is accepted by your XML parser
-  let data = req.rawBody;
-  let xmlData = data.toString();
+  const data = req.rawBody;
+  const xmlData = data.toString();
 
   const parseString = require('xml2js').parseString;
 
@@ -151,7 +151,7 @@ exports.uploadFile = (req, res) => {
     fields[fieldname] = val;
   });
 
-  let fileWrites = [];
+  const fileWrites = [];
 
   // This code will process each file uploaded.
   busboy.on('file', (fieldname, file, filename) => {
diff --git a/functions/log/index.js b/functions/log/index.js
index 58f95f3ccc..c9e76d49e1 100644
--- a/functions/log/index.js
+++ b/functions/log/index.js
@@ -61,7 +61,7 @@ function getMetrics(callback) {
   const monitoring = Monitoring.v3().metricServiceApi();
 
   // Create two datestrings, a start and end range
-  let oneWeekAgo = new Date();
+  const oneWeekAgo = new Date();
   oneWeekAgo.setHours(oneWeekAgo.getHours() - 7 * 24);
 
   const options = {
diff --git a/functions/ocr/app/index.js b/functions/ocr/app/index.js
index b67b3ff7d5..d305f67b7a 100644
--- a/functions/ocr/app/index.js
+++ b/functions/ocr/app/index.js
@@ -122,7 +122,7 @@ function renameImageForSave(filename, lang) {
  * @param {object} event (Node 8+) A Google Cloud Storage File object.
  */
 exports.processImage = event => {
-  let file = event.data || event;
+  const file = event.data || event;
 
   return Promise.resolve()
     .then(() => {
diff --git a/functions/ocr/app/test/index.test.js b/functions/ocr/app/test/index.test.js
index d2ba26d063..55e96b10a8 100644
--- a/functions/ocr/app/test/index.test.js
+++ b/functions/ocr/app/test/index.test.js
@@ -74,7 +74,7 @@ function getSample() {
     );
     stubInstance = Object.assign(stubInstance, mocks);
 
-    let out = {};
+    const out = {};
     out[property] = sinon.stub().returns(stubInstance);
     return out;
   };
diff --git a/functions/sendgrid/test/index.test.js b/functions/sendgrid/test/index.test.js
index 573b8831f7..875ee01a56 100644
--- a/functions/sendgrid/test/index.test.js
+++ b/functions/sendgrid/test/index.test.js
@@ -115,7 +115,7 @@ function getSample() {
 }
 
 function getMocks() {
-  let req = {
+  const req = {
     headers: {},
     query: {},
     body: {},
@@ -124,7 +124,7 @@ function getMocks() {
     },
   };
   sinon.spy(req, 'get');
-  let res = {
+  const res = {
     headers: {},
     send: sinon.stub().returnsThis(),
     json: sinon.stub().returnsThis(),
diff --git a/functions/speech-to-speech/functions/index.js b/functions/speech-to-speech/functions/index.js
index 086ea7a0ec..463a31501b 100644
--- a/functions/speech-to-speech/functions/index.js
+++ b/functions/speech-to-speech/functions/index.js
@@ -39,7 +39,7 @@ const textToSpeechClient = getTextToSpeechClient();
 const storageClient = getStorageClient();
 
 exports.speechTranslate = functions.https.onRequest((request, response) => {
-  let responseBody = {};
+  const responseBody = {};
 
   validateRequest(request)
     .then(() => {
@@ -70,9 +70,9 @@ exports.speechTranslate = functions.https.onRequest((request, response) => {
       responseBody.transcription = transcription;
       responseBody.gcsBucket = outputBucket;
 
-      let translations = [];
+      const translations = [];
       supportedLanguageCodes.forEach(languageCode => {
-        let translation = {languageCode: languageCode};
+        const translation = {languageCode: languageCode};
         const filenameUUID = uuid();
         const filename = filenameUUID + '.' + outputAudioEncoding.toLowerCase();
         callTextTranslation(languageCode, transcription)
diff --git a/functions/speech-to-speech/functions/test/sample.integration.http.test.js b/functions/speech-to-speech/functions/test/sample.integration.http.test.js
index 63a5f57267..026dbd32f7 100644
--- a/functions/speech-to-speech/functions/test/sample.integration.http.test.js
+++ b/functions/speech-to-speech/functions/test/sample.integration.http.test.js
@@ -123,7 +123,7 @@ describe('Tests that require a GCS bucket', function() {
         fs.readFileSync('responseBody.test.json')
       );
 
-      let deletedFiles = [];
+      const deletedFiles = [];
       // Delete the files created in the successful test.
       for (let i = 0; i < responseBody.translations.length; i++) {
         if (responseBody.translations[i].gcsPath) {
diff --git a/iot/beta-features/gateway/gateway.js b/iot/beta-features/gateway/gateway.js
index 4275dc8211..7c0030832e 100644
--- a/iot/beta-features/gateway/gateway.js
+++ b/iot/beta-features/gateway/gateway.js
@@ -326,9 +326,9 @@ function unbindDeviceFromAllGateways(
       return;
     }
 
-    let device = res.data;
+    const device = res.data;
     if (device) {
-      let isGateway = device.gatewayConfig.gatewayType === 'GATEWAY';
+      const isGateway = device.gatewayConfig.gatewayType === 'GATEWAY';
 
       if (!isGateway) {
         const listGatewaysForDeviceRequest = {
@@ -345,9 +345,9 @@ function unbindDeviceFromAllGateways(
               return;
             }
 
-            let data = res.data;
+            const data = res.data;
             if (data.devices && data.devices.length > 0) {
-              let gateways = data.devices;
+              const gateways = data.devices;
 
               gateways.forEach(gateway => {
                 const unbindRequest = {
@@ -389,17 +389,17 @@ function unbindAllDevices(client, projectId, cloudRegion, registryId) {
       console.error('Could not list devices', err);
       return;
     }
-    let data = res.data;
+    const data = res.data;
     if (!data) {
       return;
     }
 
-    let devices = data.devices;
+    const devices = data.devices;
 
     if (devices && devices.length > 0) {
       devices.forEach(device => {
         if (device) {
-          let isGateway =
+          const isGateway =
             device.gatewayConfig &&
             device.gatewayConfig.gatewayType === 'GATEWAY';
 
@@ -435,7 +435,7 @@ function listGateways(client, projectId, cloudRegion, registryId) {
       console.log('Could not list devices');
       console.log(err);
     } else {
-      let data = res.data;
+      const data = res.data;
       console.log('Current gateways in registry:');
       data.devices.forEach(function(device) {
         if (
@@ -477,7 +477,7 @@ function listDevicesForGateway(
       console.log(err);
     } else {
       console.log('Current devices bound to gateway: ', gatewayId);
-      let data = res.data;
+      const data = res.data;
       if (data.devices && data.devices.length > 0) {
         data.devices.forEach(device => {
           console.log(`\tDevice: ${device.numId} : ${device.id}`);
@@ -515,7 +515,7 @@ function listGatewaysForDevice(
       console.log(err);
     } else {
       console.log('Current gateways for device:', deviceId);
-      let data = res.data;
+      const data = res.data;
       if (data.devices && data.devices.length > 0) {
         data.devices.forEach(gateway => {
           console.log(`\tDevice: ${gateway.numId} : ${gateway.id}`);
@@ -582,7 +582,7 @@ function listenForConfigMessages(
 
   const mqttClientId = `projects/${projectId}/locations/${region}/registries/${registryId}/devices/${gatewayId}`;
   console.log(mqttClientId);
-  let connectionArgs = {
+  const connectionArgs = {
     host: mqttBridgeHostname,
     port: mqttBridgePort,
     clientId: mqttClientId,
@@ -594,7 +594,7 @@ function listenForConfigMessages(
   };
 
   // Create a client, and connect to the Google MQTT bridge.
-  let client = mqtt.connect(connectionArgs);
+  const client = mqtt.connect(connectionArgs);
 
   client.on('connect', success => {
     if (!success) {
@@ -627,7 +627,7 @@ function listenForConfigMessages(
   });
 
   client.on('message', (topic, message) => {
-    let decodedMessage = Buffer.from(message, 'base64').toString('ascii');
+    const decodedMessage = Buffer.from(message, 'base64').toString('ascii');
 
     if (topic === `/devices/${gatewayId}/errors`) {
       console.log(`message received on error topic: ${decodedMessage}`);
@@ -661,7 +661,7 @@ function listenForErrorMessages(
 
   const mqttClientId = `projects/${projectId}/locations/${region}/registries/${registryId}/devices/${gatewayId}`;
   console.log(mqttClientId);
-  let connectionArgs = {
+  const connectionArgs = {
     host: mqttBridgeHostname,
     port: mqttBridgePort,
     clientId: mqttClientId,
@@ -673,7 +673,7 @@ function listenForErrorMessages(
   };
 
   // Create a client, and connect to the Google MQTT bridge.
-  let client = mqtt.connect(connectionArgs);
+  const client = mqtt.connect(connectionArgs);
 
   client.on('connect', success => {
     if (!success) {
@@ -703,7 +703,7 @@ function listenForErrorMessages(
   });
 
   client.on('message', (topic, message) => {
-    let decodedMessage = Buffer.from(message, 'base64').toString('ascii');
+    const decodedMessage = Buffer.from(message, 'base64').toString('ascii');
 
     console.log(`message received on error topic ${topic}: ${decodedMessage}`);
   });
@@ -739,7 +739,7 @@ function sendDataFromBoundDevice(
 
   const mqttClientId = `projects/${projectId}/locations/${region}/registries/${registryId}/devices/${gatewayId}`;
   console.log(`MQTT client id: ${mqttClientId}`);
-  let connectionArgs = {
+  const connectionArgs = {
     host: mqttBridgeHostname,
     port: mqttBridgePort,
     clientId: mqttClientId,
@@ -751,8 +751,8 @@ function sendDataFromBoundDevice(
   };
 
   // Create a client, and connect to the Google MQTT bridge.
-  let iatTime = parseInt(Date.now() / 1000);
-  let client = mqtt.connect(connectionArgs);
+  const iatTime = parseInt(Date.now() / 1000);
+  const client = mqtt.connect(connectionArgs);
 
   client.on('connect', success => {
     if (!success) {
@@ -863,7 +863,7 @@ function publishAsync(
     var schedulePublishDelayMs = 5000; // messageType === 'events' ? 1000 : 2000;
     setTimeout(function() {
       // [START iot_mqtt_jwt_refresh]
-      let secsFromIssue = parseInt(Date.now() / 1000) - iatTime;
+      const secsFromIssue = parseInt(Date.now() / 1000) - iatTime;
       if (secsFromIssue > tokenExpMins * 60) {
         iatTime = parseInt(Date.now() / 1000);
         console.log(`\tRefreshing token after ${secsFromIssue} seconds.`);
diff --git a/iot/beta-features/gateway/gateway.test.js b/iot/beta-features/gateway/gateway.test.js
index cd46f8e6d3..5169cf002f 100644
--- a/iot/beta-features/gateway/gateway.test.js
+++ b/iot/beta-features/gateway/gateway.test.js
@@ -59,7 +59,7 @@ after(async () => {
 it('should create a new gateway', async () => {
   // create gateway
   const gatewayId = `nodejs-test-gateway-iot-${uuid.v4()}`;
-  let gatewayOut = await tools.runAsync(
+  const gatewayOut = await tools.runAsync(
     `${cmd} createGateway ${registryName} ${gatewayId} RS256 ${publicKeyParam}`
   ); // test no error on create gateway
   assert.strictEqual(new RegExp('Created device').test(gatewayOut), true);
@@ -78,7 +78,7 @@ it('should list gateways', async () => {
   );
 
   // look for output in list gateway
-  let gateways = await tools.runAsync(`${cmd} listGateways ${registryName}`);
+  const gateways = await tools.runAsync(`${cmd} listGateways ${registryName}`);
   assert.strictEqual(new RegExp(`${gatewayId}`).test(gateways), true);
 
   await tools.runAsync(
@@ -101,7 +101,7 @@ it('should bind existing device to gateway', async () => {
   );
 
   // bind device to gateway
-  let bind = await tools.runAsync(
+  const bind = await tools.runAsync(
     `${cmd} bindDeviceToGateway ${registryName} ${gatewayId} ${deviceId}`
   );
 
@@ -110,7 +110,7 @@ it('should bind existing device to gateway', async () => {
   assert.strictEqual(new RegExp('Could not bind device').test(bind), false);
 
   // test unbind
-  let unbind = await tools.runAsync(
+  const unbind = await tools.runAsync(
     `${cmd} unbindDeviceFromGateway ${registryName} ${gatewayId} ${deviceId}`
   );
   assert.strictEqual(new RegExp('Device no longer bound').test(unbind), true);
@@ -133,7 +133,7 @@ it('should bind new device to gateway', async () => {
 
   // binding a non-existing device should create it
   const deviceId = `nodejs-test-device-iot-${uuid.v4()}`;
-  let bind = await tools.runAsync(
+  const bind = await tools.runAsync(
     `${cmd} bindDeviceToGateway ${registryName} ${gatewayId} ${deviceId}`
   );
 
@@ -142,7 +142,7 @@ it('should bind new device to gateway', async () => {
   assert.strictEqual(new RegExp('Could not bind device').test(bind), false);
 
   // unbind and delete device and gateway
-  let unbind = await tools.runAsync(
+  const unbind = await tools.runAsync(
     `${cmd} unbindDeviceFromGateway ${registryName} ${gatewayId} ${deviceId}`
   );
   assert.strictEqual(new RegExp('Device no longer bound').test(unbind), true);
@@ -169,7 +169,7 @@ it('should list devices bound to gateway', async () => {
     `${cmd} bindDeviceToGateway ${registryName} ${gatewayId} ${deviceId}`
   );
 
-  let devices = await tools.runAsync(
+  const devices = await tools.runAsync(
     `${cmd} listDevicesForGateway ${registryName} ${gatewayId}`
   );
 
@@ -201,7 +201,7 @@ it('should list gateways for bound device', async () => {
     `${cmd} bindDeviceToGateway ${registryName} ${gatewayId} ${deviceId}`
   );
 
-  let devices = await tools.runAsync(
+  const devices = await tools.runAsync(
     `${cmd} listGatewaysForDevice ${registryName} ${deviceId}`
   );
 
@@ -237,7 +237,7 @@ it('should listen for bound device config message', async () => {
   );
 
   // listen for configuration changes
-  let out = await tools.runAsync(
+  const out = await tools.runAsync(
     `${cmd} listen ${deviceId} ${gatewayId} ${registryName} ${privateKeyParam} --clientDuration=30000`
   );
 
@@ -271,7 +271,7 @@ it('should listen for error topic messages', async () => {
   );
 
   // check error topic contains error of attaching a device that is not bound
-  let out = await tools.runAsync(
+  const out = await tools.runAsync(
     `${cmd} listenForErrors ${gatewayId} ${registryName} ${deviceId} ${privateKeyParam} --clientDuration=30000`
   );
 
@@ -306,7 +306,7 @@ it('should send data from bound device', async () => {
   );
 
   // relay telemetry on behalf of device
-  let out = await tools.runAsync(
+  const out = await tools.runAsync(
     `${cmd} relayData ${deviceId} ${gatewayId} ${registryName} ${privateKeyParam} --numMessages=5`
   );
 
diff --git a/iot/http_example/cloudiot_http_example.js b/iot/http_example/cloudiot_http_example.js
index 854fda1f9f..a843163365 100644
--- a/iot/http_example/cloudiot_http_example.js
+++ b/iot/http_example/cloudiot_http_example.js
@@ -101,7 +101,11 @@ var argv = require(`yargs`)
 // must be in the format below.
 
 let iatTime = parseInt(Date.now() / 1000);
-let authToken = createJwt(argv.projectId, argv.privateKeyFile, argv.algorithm);
+const authToken = createJwt(
+  argv.projectId,
+  argv.privateKeyFile,
+  argv.algorithm
+);
 const devicePath = `projects/${argv.projectId}/locations/${
   argv.cloudRegion
 }/registries/${argv.registryId}/devices/${argv.deviceId}`;
@@ -180,7 +184,7 @@ function publishAsync(authToken, messageCount, numMessages) {
       // If we have published fewer than numMessage messages, publish payload
       // messageCount + 1.
       setTimeout(function() {
-        let secsFromIssue = parseInt(Date.now() / 1000) - iatTime;
+        const secsFromIssue = parseInt(Date.now() / 1000) - iatTime;
         if (secsFromIssue > argv.tokenExpMins * 60) {
           iatTime = parseInt(Date.now() / 1000);
           console.log(`\tRefreshing token after ${secsFromIssue} seconds.`);
diff --git a/iot/manager/manager.js b/iot/manager/manager.js
index cb67eded5d..8885add850 100644
--- a/iot/manager/manager.js
+++ b/iot/manager/manager.js
@@ -476,7 +476,7 @@ function listDevices(client, registryId, projectId, cloudRegion) {
       console.log('Could not list devices');
       console.log(err);
     } else {
-      let data = res.data;
+      const data = res.data;
       console.log('Current devices in registry:', data['devices']);
     }
   });
@@ -501,7 +501,7 @@ function listRegistries(client, projectId, cloudRegion) {
       console.log('Could not list registries');
       console.log(err);
     } else {
-      let data = res.data;
+      const data = res.data;
       console.log('Current registries in project:\n', data['deviceRegistries']);
     }
   });
@@ -573,9 +573,9 @@ function clearRegistry(client, registryId, projectId, cloudRegion) {
       return;
     }
 
-    let data = res.data;
+    const data = res.data;
     console.log('Current devices in registry:', data['devices']);
-    let devices = data['devices'];
+    const devices = data['devices'];
 
     if (devices) {
       devices.forEach((device, index) => {
@@ -1095,9 +1095,9 @@ function unbindDeviceFromAllGateways(
       return;
     }
 
-    let device = res.data;
+    const device = res.data;
     if (device) {
-      let isGateway = device.gatewayConfig.gatewayType === 'GATEWAY';
+      const isGateway = device.gatewayConfig.gatewayType === 'GATEWAY';
 
       if (!isGateway) {
         const listGatewaysForDeviceRequest = {
@@ -1114,9 +1114,9 @@ function unbindDeviceFromAllGateways(
               return;
             }
 
-            let data = res.data;
+            const data = res.data;
             if (data.devices && data.devices.length > 0) {
-              let gateways = data.devices;
+              const gateways = data.devices;
 
               gateways.forEach(gateway => {
                 const unbindRequest = {
@@ -1159,17 +1159,17 @@ function unbindAllDevices(client, projectId, cloudRegion, registryId) {
       return;
     }
 
-    let data = res.data;
+    const data = res.data;
     if (!data) {
       return;
     }
 
-    let devices = data.devices;
+    const devices = data.devices;
 
     if (devices && devices.length > 0) {
       devices.forEach(device => {
         if (device) {
-          let isGateway =
+          const isGateway =
             device.gatewayConfig &&
             device.gatewayConfig.gatewayType === 'GATEWAY';
 
@@ -1205,7 +1205,7 @@ function listGateways(client, projectId, cloudRegion, registryId) {
       console.log('Could not list devices');
       console.log(err);
     } else {
-      let data = res.data;
+      const data = res.data;
       console.log('Current gateways in registry:');
       data.devices.forEach(function(device) {
         if (
@@ -1247,7 +1247,7 @@ function listDevicesForGateway(
       console.log(err);
     } else {
       console.log('Current devices bound to gateway: ', gatewayId);
-      let data = res.data;
+      const data = res.data;
       if (data.devices && data.devices.length > 0) {
         data.devices.forEach(device => {
           console.log(`\tDevice: ${device.numId} : ${device.id}`);
@@ -1285,7 +1285,7 @@ function listGatewaysForDevice(
       console.log(err);
     } else {
       console.log('Current gateways for device:', deviceId);
-      let data = res.data;
+      const data = res.data;
       if (data.devices && data.devices.length > 0) {
         data.devices.forEach(gateway => {
           console.log(`\tDevice: ${gateway.numId} : ${gateway.id}`);
diff --git a/iot/manager/system-test/manager.test.js b/iot/manager/system-test/manager.test.js
index 8406e3c385..90f4a4f5a3 100644
--- a/iot/manager/system-test/manager.test.js
+++ b/iot/manager/system-test/manager.test.js
@@ -46,7 +46,7 @@ before(async () => {
   console.log(`Topic ${topic.name} created.`);
 
   // Creates a registry to be used for tests.
-  let createRegistryRequest = {
+  const createRegistryRequest = {
     parent: iotClient.locationPath(projectId, region),
     deviceRegistry: {
       id: registryName,
@@ -261,7 +261,7 @@ it('should create and get an iam policy', async () => {
 });
 
 it('should create and delete a registry', async () => {
-  let createRegistryId = registryName + 'create';
+  const createRegistryId = registryName + 'create';
 
   let output = await tools.runAsync(`${cmd} setupIotTopic ${topicName}`, cwd);
   output = await tools.runAsync(
@@ -306,7 +306,7 @@ it('should send command message to device', async () => {
 
 it('should create a new gateway', async () => {
   const gatewayId = `nodejs-test-gateway-iot-${uuid.v4()}`;
-  let gatewayOut = await tools.runAsync(
+  const gatewayOut = await tools.runAsync(
     `${cmd} createGateway ${registryName} ${gatewayId} RSA_X509_PEM ${rsaPublicCert}`
   );
 
@@ -325,7 +325,7 @@ it('should list gateways', async () => {
   );
 
   // look for output in list gateway
-  let gateways = await tools.runAsync(`${cmd} listGateways ${registryName}`);
+  const gateways = await tools.runAsync(`${cmd} listGateways ${registryName}`);
   assert.strictEqual(new RegExp(`${gatewayId}`).test(gateways), true);
 
   await iotClient.deleteDevice({
@@ -349,7 +349,7 @@ it('should bind existing device to gateway', async () => {
   });
 
   // bind device to gateway
-  let bind = await tools.runAsync(
+  const bind = await tools.runAsync(
     `${cmd} bindDeviceToGateway ${registryName} ${gatewayId} ${deviceId}`
   );
 
@@ -360,7 +360,7 @@ it('should bind existing device to gateway', async () => {
   assert.strictEqual(new RegExp('Could not bind device').test(bind), false);
 
   // test unbind
-  let unbind = await tools.runAsync(
+  const unbind = await tools.runAsync(
     `${cmd} unbindDeviceFromGateway ${registryName} ${gatewayId} ${deviceId}`
   );
   assert.strictEqual(
@@ -395,7 +395,7 @@ it('should list devices bound to gateway', async () => {
     `${cmd} bindDeviceToGateway ${registryName} ${gatewayId} ${deviceId}`
   );
 
-  let devices = await tools.runAsync(
+  const devices = await tools.runAsync(
     `${cmd} listDevicesForGateway ${registryName} ${gatewayId}`
   );
 
@@ -438,7 +438,7 @@ it('should list gateways for bound device', async () => {
     `${cmd} bindDeviceToGateway ${registryName} ${gatewayId} ${deviceId}`
   );
 
-  let devices = await tools.runAsync(
+  const devices = await tools.runAsync(
     `${cmd} listGatewaysForDevice ${registryName} ${deviceId}`
   );
 
diff --git a/iot/mqtt_example/cloudiot_mqtt_example_nodejs.js b/iot/mqtt_example/cloudiot_mqtt_example_nodejs.js
index 88bbfc9243..9aae44648a 100644
--- a/iot/mqtt_example/cloudiot_mqtt_example_nodejs.js
+++ b/iot/mqtt_example/cloudiot_mqtt_example_nodejs.js
@@ -310,7 +310,7 @@ function publishAsync(
     var schedulePublishDelayMs = argv.messageType === 'events' ? 1000 : 2000;
     setTimeout(function() {
       // [START iot_mqtt_jwt_refresh]
-      let secsFromIssue = parseInt(Date.now() / 1000) - iatTime;
+      const secsFromIssue = parseInt(Date.now() / 1000) - iatTime;
       if (secsFromIssue > argv.tokenExpMins * 60) {
         iatTime = parseInt(Date.now() / 1000);
         console.log(`\tRefreshing token after ${secsFromIssue} seconds.`);
@@ -408,7 +408,7 @@ function mqttDeviceDemo(
   // non-empty. The password field is used to transmit a JWT to authorize the
   // device. The "mqtts" protocol causes the library to connect using SSL, which
   // is required for Cloud IoT Core.
-  let connectionArgs = {
+  const connectionArgs = {
     host: mqttBridgeHostname,
     port: mqttBridgePort,
     clientId: mqttClientId,
@@ -419,8 +419,8 @@ function mqttDeviceDemo(
   };
 
   // Create a client, and connect to the Google MQTT bridge.
-  let iatTime = parseInt(Date.now() / 1000);
-  let client = mqtt.connect(connectionArgs);
+  const iatTime = parseInt(Date.now() / 1000);
+  const client = mqtt.connect(connectionArgs);
 
   // Subscribe to the /devices/{device-id}/config topic to receive config updates.
   // Config updates are recommended to use QoS 1 (at least once delivery)
@@ -578,7 +578,7 @@ function publishAsyncGateway(
 
     var schedulePublishDelayMs = 5000; // messageType === 'events' ? 1000 : 2000;
     setTimeout(function() {
-      let secsFromIssue = parseInt(Date.now() / 1000) - iatTime;
+      const secsFromIssue = parseInt(Date.now() / 1000) - iatTime;
       if (secsFromIssue > tokenExpMins * 60) {
         iatTime = parseInt(Date.now() / 1000);
         console.log(`\tRefreshing token after ${secsFromIssue} seconds.`);
@@ -633,7 +633,7 @@ function sendDataFromBoundDevice(
 
   const mqttClientId = `projects/${projectId}/locations/${region}/registries/${registryId}/devices/${gatewayId}`;
   console.log(`MQTT client id: ${mqttClientId}`);
-  let connectionArgs = {
+  const connectionArgs = {
     host: mqttBridgeHostname,
     port: mqttBridgePort,
     clientId: mqttClientId,
@@ -645,8 +645,8 @@ function sendDataFromBoundDevice(
   };
 
   // Create a client, and connect to the Google MQTT bridge.
-  let iatTime = parseInt(Date.now() / 1000);
-  let client = mqtt.connect(connectionArgs);
+  const iatTime = parseInt(Date.now() / 1000);
+  const client = mqtt.connect(connectionArgs);
 
   client.on('connect', success => {
     if (!success) {
@@ -722,7 +722,7 @@ function listenForConfigMessages(
 
   const mqttClientId = `projects/${projectId}/locations/${region}/registries/${registryId}/devices/${gatewayId}`;
   console.log(mqttClientId);
-  let connectionArgs = {
+  const connectionArgs = {
     host: mqttBridgeHostname,
     port: mqttBridgePort,
     clientId: mqttClientId,
@@ -734,7 +734,7 @@ function listenForConfigMessages(
   };
 
   // Create a client, and connect to the Google MQTT bridge.
-  let client = mqtt.connect(connectionArgs);
+  const client = mqtt.connect(connectionArgs);
 
   client.on('connect', success => {
     if (!success) {
@@ -767,7 +767,7 @@ function listenForConfigMessages(
   });
 
   client.on('message', (topic, message) => {
-    let decodedMessage = Buffer.from(message, 'base64').toString('ascii');
+    const decodedMessage = Buffer.from(message, 'base64').toString('ascii');
 
     if (topic === `/devices/${gatewayId}/errors`) {
       console.log(`message received on error topic: ${decodedMessage}`);
@@ -809,7 +809,7 @@ function listenForErrorMessages(
 
   const mqttClientId = `projects/${projectId}/locations/${region}/registries/${registryId}/devices/${gatewayId}`;
   console.log(mqttClientId);
-  let connectionArgs = {
+  const connectionArgs = {
     host: mqttBridgeHostname,
     port: mqttBridgePort,
     clientId: mqttClientId,
@@ -821,7 +821,7 @@ function listenForErrorMessages(
   };
 
   // Create a client, and connect to the Google MQTT bridge.
-  let client = mqtt.connect(connectionArgs);
+  const client = mqtt.connect(connectionArgs);
 
   client.on('connect', success => {
     if (!success) {
@@ -851,7 +851,7 @@ function listenForErrorMessages(
   });
 
   client.on('message', (topic, message) => {
-    let decodedMessage = Buffer.from(message, 'base64').toString('ascii');
+    const decodedMessage = Buffer.from(message, 'base64').toString('ascii');
 
     console.log(`message received on error topic ${topic}: ${decodedMessage}`);
   });
diff --git a/iot/mqtt_example/system-test/cloudiot_mqtt_example.test.js b/iot/mqtt_example/system-test/cloudiot_mqtt_example.test.js
index 5e67a6cb23..beae599bd3 100644
--- a/iot/mqtt_example/system-test/cloudiot_mqtt_example.test.js
+++ b/iot/mqtt_example/system-test/cloudiot_mqtt_example.test.js
@@ -47,7 +47,7 @@ before(async () => {
   console.log(`Topic ${topic.name} created.`);
 
   // Creates a registry to be used for tests.
-  let createRegistryRequest = {
+  const createRegistryRequest = {
     parent: iotClient.locationPath(projectId, region),
     deviceRegistry: {
       id: registryName,
@@ -190,7 +190,7 @@ it('should receive command message', async () => {
     cwd
   );
 
-  let output = tools.runAsync(
+  const output = tools.runAsync(
     `${cmd} mqttDeviceDemo --registryId=${localRegName} --deviceId=${deviceId} --numMessages=30 --privateKeyFile=${rsaPrivateKey} --algorithm=RS256 --mqttBridgePort=443`,
     cwd
   );
@@ -228,7 +228,7 @@ it('should listen for bound device config message', async () => {
   );
 
   // listen for configuration changes
-  let out = await tools.runAsync(
+  const out = await tools.runAsync(
     `${cmd} listenForConfigMessages --deviceId=${deviceId} --gatewayId=${gatewayId} --registryId=${registryName} --privateKeyFile=${rsaPrivateKey} --clientDuration=10000 --algorithm=RS256`
   );
 
@@ -264,7 +264,7 @@ it('should listen for error topic messages', async () => {
   );
 
   // check error topic contains error of attaching a device that is not bound
-  let out = await tools.runAsync(
+  const out = await tools.runAsync(
     `${cmd} listenForErrorMessages --gatewayId=${gatewayId} --registryId=${registryName} --deviceId=${deviceId} --privateKeyFile=${rsaPrivateKey} --clientDuration=30000 --algorithm=RS256`
   );
 
@@ -309,7 +309,7 @@ it('should send data from bound device', async () => {
   );
 
   // relay telemetry on behalf of device
-  let out = await tools.runAsync(
+  const out = await tools.runAsync(
     `${cmd} sendDataFromBoundDevice --deviceId=${deviceId} --gatewayId=${gatewayId} --registryId=${registryName} --privateKeyFile=${rsaPrivateKey} --numMessages=5 --algorithm=RS256`
   );
 
diff --git a/package.json b/package.json
index 77b6d2f0e2..d73d6a251e 100644
--- a/package.json
+++ b/package.json
@@ -14,6 +14,7 @@
   "private": true,
   "scripts": {
     "lint": "eslint '**/*.js'",
+    "fix": "eslint --fix '**/*.js'",
     "test": "echo 'Please run tests in each sample directory.' && exit 1"
   },
   "devDependencies": {