diff --git a/packages/auth/src/args.js b/packages/auth/src/args.js
index 0663e041516..67f779de508 100644
--- a/packages/auth/src/args.js
+++ b/packages/auth/src/args.js
@@ -239,7 +239,7 @@ fireauth.args.string = function(opt_name, opt_optional) {
     name: opt_name || '',
     typeLabel: 'a valid string',
     optional: !!opt_optional,
-    validator: goog.isString
+    validator: x => typeof x === 'string'
   };
 };
 
@@ -256,7 +256,7 @@ fireauth.args.bool = function(opt_name, opt_optional) {
     name: opt_name || '',
     typeLabel: 'a boolean',
     optional: !!opt_optional,
-    validator: goog.isBoolean
+    validator: x => typeof x === 'boolean'
   };
 };
 
@@ -273,7 +273,7 @@ fireauth.args.number = function(opt_name, opt_optional) {
     name: opt_name || '',
     typeLabel: 'a valid number',
     optional: !!opt_optional,
-    validator: goog.isNumber
+    validator: x => typeof x === 'number'
   };
 };
 
@@ -324,7 +324,7 @@ fireauth.args.null = function(opt_name, opt_optional) {
     name: opt_name || '',
     typeLabel: 'null',
     optional: !!opt_optional,
-    validator: goog.isNull
+    validator: x => x === null
   };
 };
 
@@ -527,7 +527,7 @@ fireauth.args.phoneInfoOptions = function(name, optional) {
             return fireauth.args.validateMultiFactorSession_(
                        phoneInfoOptions['session'],
                        fireauth.MultiFactorSession.Type.ENROLL) &&
-                   goog.isString(phoneInfoOptions['phoneNumber']);
+                   typeof phoneInfoOptions['phoneNumber'] === 'string';
           // For multi-factor sign-in, phone multi-factor hint and MFA session
           // are provided.
           } else if (phoneInfoOptions['session'] &&
@@ -544,10 +544,10 @@ fireauth.args.phoneInfoOptions = function(name, optional) {
             return fireauth.args.validateMultiFactorSession_(
                        phoneInfoOptions['session'],
                        fireauth.MultiFactorSession.Type.SIGN_IN) &&
-                   goog.isString(phoneInfoOptions['multiFactorUid']);
+                   typeof phoneInfoOptions['multiFactorUid'] === 'string';
           // For single-factor sign-in, only phone number needs to be provided.
           } else if (phoneInfoOptions['phoneNumber']) {
-            return goog.isString(phoneInfoOptions['phoneNumber']);
+            return typeof phoneInfoOptions['phoneNumber'] === 'string';
           }
           return false;
         })
@@ -562,7 +562,7 @@ fireauth.args.phoneInfoOptions = function(name, optional) {
  * @private
  */
 fireauth.args.validateMultiFactorSession_ = function(session, type) {
-  return goog.isObject(session) && goog.isString(session.type) &&
+  return goog.isObject(session) && typeof session.type === 'string' &&
       session.type === type &&
       goog.isFunction(session.getRawSession);
 };
@@ -574,7 +574,7 @@ fireauth.args.validateMultiFactorSession_ = function(session, type) {
  * @private
  */
 fireauth.args.validateMultiFactorInfo_ = function(info) {
-  return goog.isObject(info) && goog.isString(info['uid']);
+  return goog.isObject(info) && typeof info['uid'] === 'string';
 };
 
 
@@ -612,7 +612,7 @@ fireauth.args.applicationVerifier = function(opt_optional) {
         /** @type {function(!firebase.auth.ApplicationVerifier) : boolean} */ (
         function(applicationVerifier) {
           return !!(applicationVerifier &&
-                    goog.isString(applicationVerifier.type) &&
+                    typeof applicationVerifier.type === 'string' &&
                     goog.isFunction(applicationVerifier.verify));
         })
   });
diff --git a/packages/auth/src/authcredential.js b/packages/auth/src/authcredential.js
index ce9a5e8c2a7..784be606bad 100644
--- a/packages/auth/src/authcredential.js
+++ b/packages/auth/src/authcredential.js
@@ -1363,7 +1363,7 @@ fireauth.PhoneAuthProvider.prototype.verifyPhoneNumber =
   // time after sending the token to the server.
   return goog.Promise.resolve(applicationVerifier['verify']())
       .then(function(assertion) {
-        if (!goog.isString(assertion)) {
+        if (typeof assertion !== 'string') {
           throw new fireauth.AuthError(fireauth.authenum.Error.ARGUMENT_ERROR,
               'An implementation of firebase.auth.ApplicationVerifier' +
               '.prototype.verify() must return a firebase.Promise ' +
@@ -1565,7 +1565,7 @@ fireauth.AuthProvider.getCredentialFromResponse = function(response) {
  * @return {?fireauth.AuthCredential} The corresponding AuthCredential.
  */
 fireauth.AuthProvider.getCredentialFromJSON = function(json) {
-  var obj = goog.isString(json) ? JSON.parse(json) : json;
+  var obj = typeof json === 'string' ? JSON.parse(json) : json;
   var credential;
   var fromJSON = [
     fireauth.OAuthCredential.fromJSON,
diff --git a/packages/auth/src/multifactoruser.js b/packages/auth/src/multifactoruser.js
index 81794caa281..ae11740039b 100644
--- a/packages/auth/src/multifactoruser.js
+++ b/packages/auth/src/multifactoruser.js
@@ -201,7 +201,7 @@ fireauth.MultiFactorUser.prototype.enroll = function(assertion, displayName) {
  */
 fireauth.MultiFactorUser.prototype.unenroll = function(target) {
   var self = this;
-  var uid = goog.isString(target) ? target : target['uid'];
+  var uid = typeof target === 'string' ? target : target['uid'];
   var rpcHandler = this.user_.getRpcHandler();
   return this.user_.getIdToken().then(function(idToken) {
     return rpcHandler.withdrawMfa(idToken, uid);
diff --git a/packages/auth/src/storage/localstorage.js b/packages/auth/src/storage/localstorage.js
index 380b4226161..3dae5f209b1 100644
--- a/packages/auth/src/storage/localstorage.js
+++ b/packages/auth/src/storage/localstorage.js
@@ -136,7 +136,7 @@ fireauth.storage.LocalStorage.prototype.set = function(key, value) {
   return goog.Promise.resolve()
       .then(function() {
         var obj = fireauth.util.stringifyJSON(value);
-        if (goog.isNull(obj)) {
+        if (obj === null) {
           self.remove(key);
         } else {
           self.storage_.setItem(key, obj);
diff --git a/packages/auth/src/storage/sessionstorage.js b/packages/auth/src/storage/sessionstorage.js
index 098282baafc..956beb2ac90 100644
--- a/packages/auth/src/storage/sessionstorage.js
+++ b/packages/auth/src/storage/sessionstorage.js
@@ -136,7 +136,7 @@ fireauth.storage.SessionStorage.prototype.set = function(key, value) {
   return goog.Promise.resolve()
       .then(function() {
         var obj = fireauth.util.stringifyJSON(value);
-        if (goog.isNull(obj)) {
+        if (obj === null) {
           self.remove(key);
         } else {
           self.storage_.setItem(key, obj);
diff --git a/packages/auth/src/utils.js b/packages/auth/src/utils.js
index 8c824f1fff7..1b8121f878d 100644
--- a/packages/auth/src/utils.js
+++ b/packages/auth/src/utils.js
@@ -482,7 +482,7 @@ fireauth.util.EMAIL_ADDRESS_REGEXP_ = /^[^@]+@[^@]+$/;
  * @return {boolean} Whether the email address is valid.
  */
 fireauth.util.isValidEmailAddress = function(email) {
-  return goog.isString(email) &&
+  return typeof email === 'string' &&
       fireauth.util.EMAIL_ADDRESS_REGEXP_.test(email);
 };
 
@@ -1140,7 +1140,7 @@ fireauth.util.removeEntriesWithKeys = function(obj, keys) {
  * @return {*} The raw object.
  */
 fireauth.util.parseJSON = function(json) {
-  if (goog.isNull(json)) {
+  if (json === null) {
     return undefined;
   }