diff --git a/build-system/compile/compile.js b/build-system/compile/compile.js
index cf803b03623f..76c55a4ec612 100644
--- a/build-system/compile/compile.js
+++ b/build-system/compile/compile.js
@@ -371,6 +371,7 @@ function compile(entryModuleFilenames, outputDir, outputFilename, options) {
       // it won't do strict type checking if its whitespace only.
       compilerOptions.define.push('TYPECHECK_ONLY=true');
       compilerOptions.jscomp_error.push(
+        'conformanceViolations',
         'checkTypes',
         'accessControls',
         'const',
diff --git a/build-system/conformance-config.textproto b/build-system/conformance-config.textproto
index 13e63537dde9..f59e3eb0516a 100644
--- a/build-system/conformance-config.textproto
+++ b/build-system/conformance-config.textproto
@@ -258,6 +258,7 @@ requirement: {
   whitelist: 'src/web-worker/web-worker.js'
   # Allowing violations in ads code for now.
   # We would have to fix this to property obfuscated the 3p frame code.
+  whitelist: '3p/iframe-messaging-client.js'
   whitelist: 'ads/google/deprecated_doubleclick.js'
   whitelist: 'ads/google/imaVideo.js'
 }
@@ -348,10 +349,11 @@ requirement: {
   whitelist: 'extensions/amp-date-picker/0.1/dates-list.js'
 }
 
-requirement: {
-  type: BANNED_PROPERTY_CALL
-  error_message: 'ChildNode.p.after() is unusual. Please use Node.p.insertBefore()'
-  value: 'Element.prototype.after'
-  value: 'DocumentType.prototype.after'
-  value: 'CharacterData.prototype.after'
-}
+# TODO(rsimha): Reenable when we move RRule to a node module.
+# requirement: {
+  # type: BANNED_PROPERTY_CALL
+  # error_message: 'ChildNode.p.after() is unusual. Please use Node.p.insertBefore()'
+  # value: 'Element.prototype.after'
+  # value: 'DocumentType.prototype.after'
+  # value: 'CharacterData.prototype.after'
+# }
diff --git a/extensions/amp-auto-ads/0.1/anchor-ad-strategy.js b/extensions/amp-auto-ads/0.1/anchor-ad-strategy.js
index b7d34de47c80..f8ce6f07cc4f 100644
--- a/extensions/amp-auto-ads/0.1/anchor-ad-strategy.js
+++ b/extensions/amp-auto-ads/0.1/anchor-ad-strategy.js
@@ -88,9 +88,9 @@ export class AnchorAdStrategy {
    * @private
    */
   isFilledAnchorAdEnabled_() {
-    return (this.configObj_['optInStatus'] || []).includes(
-      OptInStatus.OPT_IN_STATUS_ANCHOR_ADS
-    );
+    return user()
+      .assertArray(this.configObj_['optInStatus'] || [])
+      .includes(OptInStatus.OPT_IN_STATUS_ANCHOR_ADS);
   }
 
   /**
@@ -98,9 +98,9 @@ export class AnchorAdStrategy {
    * @private
    */
   isNoFillAnchorAdEnabled_() {
-    return (this.configObj_['optInStatus'] || []).includes(
-      OptInStatus.OPT_IN_STATUS_NO_FILL_ANCHOR_ADS
-    );
+    return user()
+      .assertArray(this.configObj_['optInStatus'] || [])
+      .includes(OptInStatus.OPT_IN_STATUS_NO_FILL_ANCHOR_ADS);
   }
 
   /**
diff --git a/extensions/amp-experiment/1.0/attribute-allow-list/allowed-attribute-mutation-entry.js b/extensions/amp-experiment/1.0/attribute-allow-list/allowed-attribute-mutation-entry.js
index 04fdba8effeb..9236e0de726c 100644
--- a/extensions/amp-experiment/1.0/attribute-allow-list/allowed-attribute-mutation-entry.js
+++ b/extensions/amp-experiment/1.0/attribute-allow-list/allowed-attribute-mutation-entry.js
@@ -30,9 +30,7 @@ export class AllowedAttributeMutationEntry {
    * @return {boolean}
    */
   validate(mutationRecord) {
-    if (mutationRecord['value']) {
-      return true;
-    }
+    return !!mutationRecord['value'];
   }
 
   /**
diff --git a/extensions/amp-geo/0.1/amp-geo.js b/extensions/amp-geo/0.1/amp-geo.js
index 30f703f3042a..a8107fe2a50d 100644
--- a/extensions/amp-geo/0.1/amp-geo.js
+++ b/extensions/amp-geo/0.1/amp-geo.js
@@ -343,7 +343,9 @@ export class AmpGeo extends AMP.BaseElement {
               const {classList} = body;
               // Always remove the pending class
               classesToRemove.push('amp-geo-pending');
-              classesToRemove.forEach(toRemove => classList.remove(toRemove));
+              classesToRemove.forEach(toRemove => {
+                /** @type {!DOMTokenList} */ (classList).remove(toRemove);
+              });
 
               // add the new classes to <body>
               classesToAdd.forEach(toAdd => classList.add(toAdd));
diff --git a/extensions/amp-story/1.0/page-advancement.js b/extensions/amp-story/1.0/page-advancement.js
index f94c4ce01270..87a0fe9cd556 100644
--- a/extensions/amp-story/1.0/page-advancement.js
+++ b/extensions/amp-story/1.0/page-advancement.js
@@ -541,9 +541,10 @@ class ManualAdvancement extends AdvancementConfig {
    */
   isHandledByEmbeddedComponent_(event, pageRect) {
     const target = dev().assertElement(event.target);
-    const inExpandedMode =
-      this.storeService_.get(StateProperty.INTERACTIVE_COMPONENT_STATE)
-        .state === EmbeddedComponentState.EXPANDED;
+    const stored = /** @type {InteractiveComponentDef} */ (this.storeService_.get(
+      StateProperty.INTERACTIVE_COMPONENT_STATE
+    ));
+    const inExpandedMode = stored.state === EmbeddedComponentState.EXPANDED;
 
     return (
       inExpandedMode ||