diff --git a/.eslintrc.js b/.eslintrc.js
index f973206d168319..36dc6d489f5cfb 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -15,6 +15,7 @@ module.exports = {
     // Enabled checks.
     'brace-style': ['error', '1tbs'],
     'curly': ['error', 'multi-line', 'consistent'],
+    'no-extra-boolean-cast': 'error',
     'no-extra-semi': 'error',
     'no-new-wrappers': 'error',
     'no-restricted-properties': [
diff --git a/chrome/browser/resources/bookmarks/item.js b/chrome/browser/resources/bookmarks/item.js
index 18fb94f0ad0c34..82dd723fa33459 100644
--- a/chrome/browser/resources/bookmarks/item.js
+++ b/chrome/browser/resources/bookmarks/item.js
@@ -59,9 +59,9 @@ Polymer({
 
   /** @override */
   attached: function() {
-    this.watch('item_', (store) => store.nodes[this.itemId]);
+    this.watch('item_', store => store.nodes[this.itemId]);
     this.watch(
-        'isSelectedItem_', (store) => !!store.selection.items.has(this.itemId));
+        'isSelectedItem_', store => store.selection.items.has(this.itemId));
 
     this.updateFromStore();
   },
diff --git a/chrome/browser/resources/chromeos/chromevox/common/dom_util.js b/chrome/browser/resources/chromeos/chromevox/common/dom_util.js
index 47a4aa7b8cbb4e..70cd5a280b396a 100644
--- a/chrome/browser/resources/chromeos/chromevox/common/dom_util.js
+++ b/chrome/browser/resources/chromeos/chromevox/common/dom_util.js
@@ -371,7 +371,7 @@ cvox.DomUtil.isLeafNode = function(node, opt_allowHidden) {
       return true;
   }
 
-  if (!!cvox.DomPredicates.linkPredicate([element])) {
+  if (cvox.DomPredicates.linkPredicate([element])) {
     return !cvox.DomUtil.findNode(element, function(node) {
       return !!cvox.DomPredicates.headingPredicate([node]);
     });
@@ -584,9 +584,9 @@ cvox.DomUtil.getName = function(
  * @private
  */
 cvox.DomUtil.hasChildrenBasedName_ = function(node, opt_allowHidden) {
-  if (!!cvox.DomPredicates.linkPredicate([node]) ||
-      !!cvox.DomPredicates.headingPredicate([node]) ||
-      node.tagName == 'BUTTON' || cvox.AriaUtil.isControlWidget(node) ||
+  if (cvox.DomPredicates.linkPredicate([node]) ||
+      cvox.DomPredicates.headingPredicate([node]) || node.tagName == 'BUTTON' ||
+      cvox.AriaUtil.isControlWidget(node) ||
       !cvox.DomUtil.isLeafNode(node, opt_allowHidden)) {
     return true;
   } else {
@@ -1112,7 +1112,7 @@ cvox.DomUtil.computeHasContent_ = function(node) {
     }
   }
 
-  if (!!cvox.DomPredicates.linkPredicate([node])) {
+  if (cvox.DomPredicates.linkPredicate([node])) {
     return true;
   }
 
diff --git a/chrome/browser/resources/chromeos/chromevox/cvox2/background/automation_predicate.js b/chrome/browser/resources/chromeos/chromevox/cvox2/background/automation_predicate.js
index 4b1591c349926b..44bbe88b3938f1 100644
--- a/chrome/browser/resources/chromeos/chromevox/cvox2/background/automation_predicate.js
+++ b/chrome/browser/resources/chromeos/chromevox/cvox2/background/automation_predicate.js
@@ -440,12 +440,12 @@ AutomationPredicate.shouldIgnoreNode = function(node) {
 
   // Ignore nodes acting as labels for another control, that don't
   // have actionable descendants.
-  if (!!node.labelFor && node.labelFor.length > 0 &&
+  if (node.labelFor && node.labelFor.length > 0 &&
       !hasActionableDescendant(node))
     return true;
 
   // Similarly, ignore nodes acting as descriptions.
-  if (!!node.descriptionFor && node.descriptionFor.length > 0 &&
+  if (node.descriptionFor && node.descriptionFor.length > 0 &&
       !hasActionableDescendant(node))
     return true;
 
diff --git a/chrome/browser/resources/chromeos/internet_detail_dialog/internet_detail_dialog.js b/chrome/browser/resources/chromeos/internet_detail_dialog/internet_detail_dialog.js
index 5ecdaa20177937..32372f42b22242 100644
--- a/chrome/browser/resources/chromeos/internet_detail_dialog/internet_detail_dialog.js
+++ b/chrome/browser/resources/chromeos/internet_detail_dialog/internet_detail_dialog.js
@@ -126,7 +126,7 @@ Polymer({
    * @private
    */
   getNetworkDetails_: function() {
-    assert(!!this.guid);
+    assert(this.guid);
     this.networkingPrivate.getManagedProperties(
         this.guid, this.getPropertiesCallback_.bind(this));
   },
@@ -167,7 +167,7 @@ Polymer({
     if (!this.networkPropertiesReceived_)
       return;
 
-    assert(!!this.guid);
+    assert(this.guid);
     this.networkingPrivate.setProperties(this.guid, onc, () => {
       if (chrome.runtime.lastError) {
         // An error typically indicates invalid input; request the properties
@@ -487,7 +487,7 @@ Polymer({
   getInfoFields_: function() {
     /** @type {!Array<string>} */ var fields = [];
     var type = this.networkProperties.Type;
-    if (type == CrOnc.Type.CELLULAR && !!this.networkProperties.Cellular) {
+    if (type == CrOnc.Type.CELLULAR && this.networkProperties.Cellular) {
       fields.push(
           'Cellular.HomeProvider.Name', 'Cellular.ServingOperator.Name',
           'Cellular.ActivationState', 'Cellular.RoamingState',
diff --git a/chrome/browser/resources/chromeos/wallpaper_manager/js/event_page.js b/chrome/browser/resources/chromeos/wallpaper_manager/js/event_page.js
index 35ffb173a1ae5c..4e6e21b86a57c7 100644
--- a/chrome/browser/resources/chromeos/wallpaper_manager/js/event_page.js
+++ b/chrome/browser/resources/chromeos/wallpaper_manager/js/event_page.js
@@ -310,7 +310,7 @@ chrome.storage.onChanged.addListener(function(changes, namespace) {
         var wpDocument = wallpaperPickerWindow.contentWindow.document;
         var messageContainer = wpDocument.querySelector('#message-container');
 
-        if (!!appName) {
+        if (appName) {
           chrome.wallpaperPrivate.getStrings(function(strings) {
             var message =
                 strings.currentWallpaperSetByMessage.replace(/\$1/g, appName);
diff --git a/chrome/browser/resources/chromeos/wallpaper_manager/js/wallpaper_manager.js b/chrome/browser/resources/chromeos/wallpaper_manager/js/wallpaper_manager.js
index 8e0926ecbbfda3..5f856017ee5cd7 100644
--- a/chrome/browser/resources/chromeos/wallpaper_manager/js/wallpaper_manager.js
+++ b/chrome/browser/resources/chromeos/wallpaper_manager/js/wallpaper_manager.js
@@ -379,7 +379,7 @@ WallpaperManager.prototype.postDownloadDomInit_ = function() {
   };
 
   getThirdPartyAppName(function(appName) {
-    if (!!appName) {
+    if (appName) {
       $('message-container').textContent =
           loadTimeData.getStringF('currentWallpaperSetByMessage', appName);
       $('message-container').style.visibility = 'visible';
diff --git a/chrome/browser/resources/hangout_services/thunk.js b/chrome/browser/resources/hangout_services/thunk.js
index e2b2042297e78c..788ba4d741b728 100644
--- a/chrome/browser/resources/hangout_services/thunk.js
+++ b/chrome/browser/resources/hangout_services/thunk.js
@@ -287,7 +287,7 @@ function onProcessCpu(port) {
       } else if (process.type == 'gpu') {
         gpuProcessCpu = process.cpu;
       }
-      if (!!browserProcessCpu && !!gpuProcessCpu) {
+      if (browserProcessCpu && gpuProcessCpu) {
         break;
       }
     }
diff --git a/chrome/browser/resources/local_ntp/custom_links_edit.js b/chrome/browser/resources/local_ntp/custom_links_edit.js
index 485222881fb849..d512f33619bedc 100644
--- a/chrome/browser/resources/local_ntp/custom_links_edit.js
+++ b/chrome/browser/resources/local_ntp/custom_links_edit.js
@@ -152,7 +152,7 @@ function finishEditLink() {
   }
 
   // Update the link only if a field was changed.
-  if (!!newUrl || !!newTitle) {
+  if (newUrl || newTitle) {
     chrome.embeddedSearch.newTabPage.updateCustomLink(
         prepopulatedLink.rid, newUrl, newTitle);
   }
diff --git a/chrome/browser/resources/local_ntp/doodles.js b/chrome/browser/resources/local_ntp/doodles.js
index 9708c8a7d8143b..89ec7af9f9d963 100644
--- a/chrome/browser/resources/local_ntp/doodles.js
+++ b/chrome/browser/resources/local_ntp/doodles.js
@@ -396,7 +396,7 @@ doodles.showLogoOrDoodle = function(fromCache) {
           .classList.remove(doodles.CLASSES.SHOW_LOGO);
 
       // Log the impression in Chrome metrics.
-      var isCta = !!doodles.targetDoodle.metadata.animatedUrl;
+      var isCta = doodles.targetDoodle.metadata.animatedUrl;
       var eventType = isCta ?
           (fromCache ? doodles.LOG_TYPE.NTP_CTA_LOGO_SHOWN_FROM_CACHE :
                        doodles.LOG_TYPE.NTP_CTA_LOGO_SHOWN_FRESH) :
diff --git a/chrome/browser/resources/local_ntp/voice.js b/chrome/browser/resources/local_ntp/voice.js
index 7d34f80a791cbb..106dfe7d0743b1 100644
--- a/chrome/browser/resources/local_ntp/voice.js
+++ b/chrome/browser/resources/local_ntp/voice.js
@@ -538,7 +538,7 @@ speech.handleRecognitionResult_ = function(responseEvent) {
 
   // Force-stop long queries.
   if (speech.interimResult_.length > speech.QUERY_LENGTH_LIMIT_) {
-    if (!!speech.finalResult_) {
+    if (speech.finalResult_) {
       speech.submitFinalResult_();
     } else {
       speech.onErrorReceived_(RecognitionError.NO_MATCH);
@@ -749,7 +749,7 @@ speech.onKeyDown = function(event) {
  * @private
  */
 speech.onIdleTimeout_ = function() {
-  if (!!speech.finalResult_) {
+  if (speech.finalResult_) {
     speech.submitFinalResult_();
     return;
   }
@@ -1167,7 +1167,7 @@ text.showErrorMessage = function(error) {
 
   const linkElement = text.getErrorLink_(error);
   // Setting textContent removes all children (no need to clear link elements).
-  if (!!linkElement) {
+  if (linkElement) {
     text.interim_.textContent += ' ';
     text.interim_.appendChild(linkElement);
   }
diff --git a/chrome/browser/resources/media_router/elements/media_router_container/media_router_container.js b/chrome/browser/resources/media_router/elements/media_router_container/media_router_container.js
index 9788ae48a2eb7e..830b41b4517e16 100644
--- a/chrome/browser/resources/media_router/elements/media_router_container/media_router_container.js
+++ b/chrome/browser/resources/media_router/elements/media_router_container/media_router_container.js
@@ -799,7 +799,7 @@ Polymer({
    * @private
    */
   computeIssueBannerClass_: function(issue) {
-    return !!issue && !issue.isBlocking ? 'non-blocking' : '';
+    return issue && !issue.isBlocking ? 'non-blocking' : '';
   },
 
   /**
@@ -1374,7 +1374,7 @@ Polymer({
    * @private
    */
   maybeShowIssueView_: function(issue) {
-    if (!!issue) {
+    if (issue) {
       if (issue.isBlocking) {
         this.currentView_ = media_router.MediaRouterView.ISSUE;
       } else if (this.currentView_ == media_router.MediaRouterView.SINK_LIST) {
@@ -1389,7 +1389,7 @@ Polymer({
       this.showSinkList_();
     }
 
-    if (!!this.pendingCreatedRouteId_ && !!issue &&
+    if (this.pendingCreatedRouteId_ && issue &&
         issue.routeId == this.pendingCreatedRouteId_) {
       this.resetRouteCreationProperties_(false);
     }
diff --git a/chrome/browser/resources/print_preview/new/destination_dialog.js b/chrome/browser/resources/print_preview/new/destination_dialog.js
index 9cceebda4a5ae9..2aae2bd227be5c 100644
--- a/chrome/browser/resources/print_preview/new/destination_dialog.js
+++ b/chrome/browser/resources/print_preview/new/destination_dialog.js
@@ -214,7 +214,7 @@ Polymer({
                 'Failed to resolve provisional destination: ' + destination.id);
           })
           .then(() => {
-            if (this.$.dialog.open && !!listItem && !listItem.hidden) {
+            if (this.$.dialog.open && listItem && !listItem.hidden) {
               listItem.focus();
             }
           });
diff --git a/chrome/browser/resources/print_preview/new/model.js b/chrome/browser/resources/print_preview/new/model.js
index 5c646aeb5a39cb..e1fe997724f418 100644
--- a/chrome/browser/resources/print_preview/new/model.js
+++ b/chrome/browser/resources/print_preview/new/model.js
@@ -369,7 +369,7 @@ Polymer({
 
     this.lastDestinationCapabilities_ = this.destination.capabilities;
 
-    const caps = !!this.destination.capabilities ?
+    const caps = this.destination.capabilities ?
         this.destination.capabilities.printer :
         null;
     this.updateSettingsAvailabilityFromDestination_(caps);
@@ -386,8 +386,8 @@ Polymer({
    * @private
    */
   updateSettingsAvailabilityFromDestination_: function(caps) {
-    this.set('settings.copies.available', !!caps && !!(caps.copies));
-    this.set('settings.collate.available', !!caps && !!(caps.collate));
+    this.set('settings.copies.available', !!caps && !!caps.copies);
+    this.set('settings.collate.available', !!caps && !!caps.collate);
     this.set('settings.layout.available', this.isLayoutAvailable_(caps));
     this.set('settings.color.available', this.destination.hasColorCapability);
 
@@ -424,7 +424,7 @@ Polymer({
         'settings.fitToPage.available',
         !knownSizeToSaveAsPdf && !this.documentSettings.isModifiable);
     this.set('settings.scaling.available', !knownSizeToSaveAsPdf);
-    const caps = (!!this.destination && !!this.destination.capabilities) ?
+    const caps = this.destination && this.destination.capabilities ?
         this.destination.capabilities.printer :
         null;
     this.set(
@@ -602,17 +602,17 @@ Polymer({
       const vendorSettings = {};
       for (const item of caps.vendor_capability) {
         let defaultValue = null;
-        if (item.type == 'SELECT' && !!item.select_cap &&
-            !!item.select_cap.option) {
+        if (item.type == 'SELECT' && item.select_cap &&
+            item.select_cap.option) {
           const defaultOption =
               item.select_cap.option.find(o => !!o.is_default);
-          defaultValue = !!defaultOption ? defaultOption.value : null;
+          defaultValue = defaultOption ? defaultOption.value : null;
         } else if (item.type == 'RANGE') {
-          if (!!item.range_cap) {
+          if (item.range_cap) {
             defaultValue = item.range_cap.default || null;
           }
         } else if (item.type == 'TYPED_VALUE') {
-          if (!!item.typed_value_cap) {
+          if (item.typed_value_cap) {
             defaultValue = item.typed_value_cap.default || null;
           }
         }
diff --git a/chrome/browser/resources/print_preview/new/preview_area.js b/chrome/browser/resources/print_preview/new/preview_area.js
index cf769837acde9b..a975619aa00cc6 100644
--- a/chrome/browser/resources/print_preview/new/preview_area.js
+++ b/chrome/browser/resources/print_preview/new/preview_area.js
@@ -570,7 +570,7 @@ Polymer({
     const newValue =
         /** @type {!print_preview.MarginsSetting} */ (
             this.getSettingValue('customMargins'));
-    if (!!this.lastCustomMargins_ &&
+    if (this.lastCustomMargins_ &&
         this.lastCustomMargins_.marginTop !== undefined &&
         this.getSettingValue('margins') ==
             print_preview.ticket_items.MarginsTypeValue.CUSTOM &&
@@ -588,7 +588,7 @@ Polymer({
     const newValue =
         /** @type {!print_preview_new.MediaSizeValue} */ (
             this.getSettingValue('mediaSize'));
-    if (!!this.lastMediaSize_ &&
+    if (this.lastMediaSize_ &&
         (newValue.height_microns != this.lastMediaSize_.height_microns ||
          newValue.width_microns != this.lastMediaSize_.width_microns)) {
       this.onSettingsChanged_();
diff --git a/chrome/browser/resources/print_preview/new/settings_behavior.js b/chrome/browser/resources/print_preview/new/settings_behavior.js
index f85f5b15461e7a..5935aa4ae058db 100644
--- a/chrome/browser/resources/print_preview/new/settings_behavior.js
+++ b/chrome/browser/resources/print_preview/new/settings_behavior.js
@@ -60,7 +60,7 @@ const SettingsBehavior = {
   getSetting: function(settingName) {
     const setting = /** @type {print_preview_new.Setting} */ (
         this.get(settingName, this.settings));
-    assert(!!setting, 'Setting is missing: ' + settingName);
+    assert(setting, 'Setting is missing: ' + settingName);
     return setting;
   },
 
diff --git a/chrome/browser/resources/settings/autofill_page/passwords_export_dialog.js b/chrome/browser/resources/settings/autofill_page/passwords_export_dialog.js
index 2ac79b56322660..094f607d63340d 100644
--- a/chrome/browser/resources/settings/autofill_page/passwords_export_dialog.js
+++ b/chrome/browser/resources/settings/autofill_page/passwords_export_dialog.js
@@ -125,7 +125,7 @@ Polymer({
     // time (|delayedCompletionToken_| is not null) progress should be cached
     // for consumption when the blocking time ends.
     const progressBlocked =
-        !this.progressTaskToken_ && !!this.delayedCompletionToken_;
+        !this.progressTaskToken_ && this.delayedCompletionToken_;
     if (!progressBlocked) {
       clearTimeout(this.progressTaskToken_);
       this.progressTaskToken_ = null;
@@ -245,4 +245,4 @@ Polymer({
     this.close();
   },
 });
-})();
\ No newline at end of file
+})();
diff --git a/chrome/browser/resources/settings/device_page/stylus.js b/chrome/browser/resources/settings/device_page/stylus.js
index b394aedf27ec38..1ee8863dbdfcf2 100644
--- a/chrome/browser/resources/settings/device_page/stylus.js
+++ b/chrome/browser/resources/settings/device_page/stylus.js
@@ -141,7 +141,7 @@ Polymer({
    * @private
    */
   toggleLockScreenSupport_: function() {
-    assert(!!this.selectedApp_);
+    assert(this.selectedApp_);
     if (this.selectedApp_.lockScreenSupport !=
             settings.NoteAppLockScreenSupport.ENABLED &&
         this.selectedApp_.lockScreenSupport !=
diff --git a/chrome/browser/resources/settings/internet_page/internet_detail_page.js b/chrome/browser/resources/settings/internet_page/internet_detail_page.js
index e9542a6a11c3d1..5d6af27b9670cf 100644
--- a/chrome/browser/resources/settings/internet_page/internet_detail_page.js
+++ b/chrome/browser/resources/settings/internet_page/internet_detail_page.js
@@ -350,7 +350,7 @@ Polymer({
    * @private
    */
   getNetworkDetails_: function() {
-    assert(!!this.guid);
+    assert(this.guid);
     if (this.isSecondaryUser_) {
       this.networkingPrivate.getState(
           this.guid, this.getStateCallback_.bind(this));
@@ -434,7 +434,7 @@ Polymer({
       return;
     }
 
-    assert(!!this.guid);
+    assert(this.guid);
     this.networkingPrivate.setProperties(this.guid, onc, () => {
       if (chrome.runtime.lastError) {
         // An error typically indicates invalid input; request the properties
diff --git a/chrome/browser/resources/settings/internet_page/internet_page.js b/chrome/browser/resources/settings/internet_page/internet_page.js
index 8b500c43d00df2..827a46e169d7f0 100644
--- a/chrome/browser/resources/settings/internet_page/internet_page.js
+++ b/chrome/browser/resources/settings/internet_page/internet_page.js
@@ -394,7 +394,7 @@ Polymer({
   onDeviceStatesChanged_: function(newValue, oldValue) {
     const wifiDeviceState = this.getDeviceState_(CrOnc.Type.WI_FI, newValue);
     let managedNetworkAvailable = false;
-    if (!!wifiDeviceState) {
+    if (wifiDeviceState) {
       managedNetworkAvailable = !!wifiDeviceState.ManagedNetworkAvailable;
     }
 
diff --git a/chrome/browser/resources/settings/internet_page/internet_subpage.js b/chrome/browser/resources/settings/internet_page/internet_subpage.js
index 4ca60595eb0f5f..82ddb712e80f13 100644
--- a/chrome/browser/resources/settings/internet_page/internet_subpage.js
+++ b/chrome/browser/resources/settings/internet_page/internet_subpage.js
@@ -545,6 +545,7 @@ Polymer({
 
   /**
    * @param {!CrOnc.NetworkStateProperties} state The network state.
+   * @return {boolean}
    * @private
    */
   isBlockedByPolicy_: function(state) {
diff --git a/chrome/browser/resources/settings/languages_page/languages.js b/chrome/browser/resources/settings/languages_page/languages.js
index 2bf2bbd00685fb..5408936fd7e38e 100644
--- a/chrome/browser/resources/settings/languages_page/languages.js
+++ b/chrome/browser/resources/settings/languages_page/languages.js
@@ -348,10 +348,10 @@ Polymer({
       const languageState = this.languages.enabled[i];
       this.set(
           `languages.enabled.${i}.spellCheckEnabled`,
-          !!spellCheckSet.has(languageState.language.code));
+          spellCheckSet.has(languageState.language.code));
       this.set(
           `languages.enabled.${i}.isManaged`,
-          !!spellCheckForcedSet.has(languageState.language.code));
+          spellCheckForcedSet.has(languageState.language.code));
     }
 
     this.set(
@@ -547,11 +547,11 @@ Polymer({
       }
       const languageState = /** @type {LanguageState} */ ({});
       languageState.language = language;
-      languageState.spellCheckEnabled = !!spellCheckSet.has(code);
+      languageState.spellCheckEnabled = spellCheckSet.has(code);
       languageState.translateEnabled = this.isTranslateEnabled_(
           code, !!language.supportsTranslate, translateBlockedSet,
           translateTarget, prospectiveUILanguage);
-      languageState.isManaged = !!spellCheckForcedSet.has(code);
+      languageState.isManaged = spellCheckForcedSet.has(code);
       languageState.downloadDictionaryFailureCount = 0;
       enabledLanguageStates.push(languageState);
     }
diff --git a/chrome/browser/resources/settings/people_page/people_page.js b/chrome/browser/resources/settings/people_page/people_page.js
index bdff0413abe500..fd39f74b526ae5 100644
--- a/chrome/browser/resources/settings/people_page/people_page.js
+++ b/chrome/browser/resources/settings/people_page/people_page.js
@@ -494,8 +494,8 @@ Polymer({
    * @return {Element|null}
    */
   getAdvancedSyncSettingsAssociatedControl_: function() {
-    return !!this.unifiedConsentEnabled_ ? this.$$('#sync-setup') :
-                                           this.$$('#sync-status');
+    return this.unifiedConsentEnabled_ ? this.$$('#sync-setup') :
+                                         this.$$('#sync-status');
   },
 
   /**
diff --git a/chrome/browser/resources/settings/people_page/sync_account_control.js b/chrome/browser/resources/settings/people_page/sync_account_control.js
index 0d00c38d41592a..d3f4d1cf275dea 100644
--- a/chrome/browser/resources/settings/people_page/sync_account_control.js
+++ b/chrome/browser/resources/settings/people_page/sync_account_control.js
@@ -190,7 +190,7 @@ Polymer({
    * @private
    */
   getPromoHeaderClass_: function() {
-    return !!this.subLabel_ ? 'two-line': '';
+    return this.subLabel_ ? 'two-line' : '';
   },
 
   /**
@@ -210,7 +210,7 @@ Polymer({
    * @private
    */
   getAccountLabel_: function(label, account) {
-    if(!!this.unifiedConsentEnabled && !!this.syncStatus.setupInProgress) {
+    if (this.unifiedConsentEnabled && this.syncStatus.setupInProgress) {
       return this.syncStatus.statusText || account;
     }
     return this.syncStatus.signedIn && !this.syncStatus.hasError &&
@@ -235,16 +235,16 @@ Polymer({
    * @private
    */
   getSyncIconStyle_: function() {
-    if (!!this.syncStatus.hasUnrecoverableError) {
+    if (this.syncStatus.hasUnrecoverableError) {
       return 'sync-problem';
     }
-    if (!!this.syncStatus.hasError) {
+    if (this.syncStatus.hasError) {
       return this.syncStatus.statusAction ==
               settings.StatusAction.REAUTHENTICATE ?
           'sync-paused' :
           'sync-problem';
     }
-    if (!!this.syncStatus.disabled) {
+    if (this.syncStatus.disabled) {
       return 'sync-disabled';
     }
     return 'sync';
diff --git a/chrome/browser/resources/settings/people_page/sync_controls.js b/chrome/browser/resources/settings/people_page/sync_controls.js
index 5ba595a4a03eec..c3642e29af1ed9 100644
--- a/chrome/browser/resources/settings/people_page/sync_controls.js
+++ b/chrome/browser/resources/settings/people_page/sync_controls.js
@@ -171,8 +171,8 @@ Polymer({
 
     // Navigate to main sync page when the sync controls page should *not* be
     // available.
-    if (!syncStatus.signedIn || !!syncStatus.disabled ||
-        (!!syncStatus.hasError &&
+    if (!syncStatus.signedIn || syncStatus.disabled ||
+        (syncStatus.hasError &&
          syncStatus.statusAction !== settings.StatusAction.ENTER_PASSPHRASE)) {
       settings.navigateTo(settings.routes.SYNC);
     }
diff --git a/chrome/browser/resources/settings/people_page/sync_page.js b/chrome/browser/resources/settings/people_page/sync_page.js
index ae8ffa13afe80a..98bb18b5b9104e 100644
--- a/chrome/browser/resources/settings/people_page/sync_page.js
+++ b/chrome/browser/resources/settings/people_page/sync_page.js
@@ -295,7 +295,7 @@ Polymer({
       // When the user is about to cancel the sync setup, but hasn't confirmed
       // the cancellation, navigate back and show the 'Cancel sync?' dialog.
       if (this.unifiedConsentEnabled && this.syncStatus &&
-          !!this.syncStatus.setupInProgress && this.didAbort_ &&
+          this.syncStatus.setupInProgress && this.didAbort_ &&
           !this.setupCancelConfirmed_) {
         chrome.metricsPrivate.recordUserAction(
             'Signin_Signin_BackOnAdvancedSyncSettings');
@@ -346,7 +346,7 @@ Polymer({
         // When the user tries to leave the sync setup, show the 'Leave site'
         // dialog.
         if (this.unifiedConsentEnabled && this.syncStatus &&
-            !!this.syncStatus.setupInProgress) {
+            this.syncStatus.setupInProgress) {
           event.preventDefault();
           event.returnValue = '';
 
diff --git a/chrome/browser/resources/settings/route.js b/chrome/browser/resources/settings/route.js
index 8d46e3b0d72a50..74f3bc6b704e14 100644
--- a/chrome/browser/resources/settings/route.js
+++ b/chrome/browser/resources/settings/route.js
@@ -528,7 +528,7 @@ cr.define('settings', function() {
           Object.keys(this.routes_)
               .find((key) => this.routes_[key].path == canonicalPath);
 
-      return !!matchingKey ? this.routes_[matchingKey] : null;
+      return matchingKey ? this.routes_[matchingKey] : null;
     }
 
     /**
diff --git a/chrome/browser/resources/settings/settings_page/settings_animated_pages.js b/chrome/browser/resources/settings/settings_page/settings_animated_pages.js
index df3e811554b0fc..4f0bd127e1a098 100644
--- a/chrome/browser/resources/settings/settings_page/settings_animated_pages.js
+++ b/chrome/browser/resources/settings/settings_page/settings_animated_pages.js
@@ -61,9 +61,9 @@ Polymer({
     //  1) Not a direct navigation (such that the search box stays focused), and
     //  2) Not a "back" navigation, in which case the anchor element should be
     //     focused (further below in this function).
-    if (!!this.previousRoute_ && !settings.lastRouteChangeWasPopstate()) {
+    if (this.previousRoute_ && !settings.lastRouteChangeWasPopstate()) {
       const subpage = this.querySelector('settings-subpage.iron-selected');
-      if (!!subpage) {
+      if (subpage) {
         subpage.initialFocus();
         return;
       }
diff --git a/chrome/browser/resources/settings/settings_page/settings_subpage.js b/chrome/browser/resources/settings/settings_page/settings_subpage.js
index 132cfcbf6c80b0..13a61bdfe08751 100644
--- a/chrome/browser/resources/settings/settings_page/settings_subpage.js
+++ b/chrome/browser/resources/settings/settings_page/settings_subpage.js
@@ -64,7 +64,7 @@ Polymer({
 
   /** @override */
   attached: function() {
-    if (!!this.searchLabel) {
+    if (this.searchLabel) {
       // |searchLabel| should not change dynamically.
       this.listen(this, 'clear-subpage-search', 'onClearSubpageSearch_');
     }
@@ -72,7 +72,7 @@ Polymer({
 
   /** @override */
   detached: function() {
-    if (!!this.searchLabel) {
+    if (this.searchLabel) {
       // |searchLabel| should not change dynamically.
       this.unlisten(this, 'clear-subpage-search', 'onClearSubpageSearch_');
     }
diff --git a/chrome/test/data/webui/print_preview/cloud_print_interface_stub.js b/chrome/test/data/webui/print_preview/cloud_print_interface_stub.js
index ba88658a24cb8c..0e68050dd851cc 100644
--- a/chrome/test/data/webui/print_preview/cloud_print_interface_stub.js
+++ b/chrome/test/data/webui/print_preview/cloud_print_interface_stub.js
@@ -95,7 +95,7 @@ cr.define('print_preview', function() {
           this.initialized_ = true;
         }
       }
-      if (!!printer) {
+      if (printer) {
         printer.capabilities =
             print_preview_test_utils.getCddTemplate(printerId);
         this.eventTarget_.dispatchEvent(new CustomEvent(
diff --git a/ui/webui/resources/js/cr/ui/focus_row_behavior.js b/ui/webui/resources/js/cr/ui/focus_row_behavior.js
index dab933ddea43c3..66ddbf96465e9c 100644
--- a/ui/webui/resources/js/cr/ui/focus_row_behavior.js
+++ b/ui/webui/resources/js/cr/ui/focus_row_behavior.js
@@ -125,7 +125,7 @@ cr.define('cr.ui', function() {
 
       Polymer.RenderStatus.afterNextRender(this, function() {
         const rowContainer = this.root.querySelector('[focus-row-container]');
-        assert(!!rowContainer);
+        assert(rowContainer);
         this.row_ = new VirtualFocusRow(
             rowContainer, new FocusRowBehaviorDelegate(this));
         this.ironListTabIndexChanged_();
diff --git a/ui/webui/resources/js/cr/ui/menu.js b/ui/webui/resources/js/cr/ui/menu.js
index 7d320f508b1726..bdc855eaede26d 100644
--- a/ui/webui/resources/js/cr/ui/menu.js
+++ b/ui/webui/resources/js/cr/ui/menu.js
@@ -199,7 +199,7 @@ cr.define('cr.ui', function() {
       if (menuItem.hidden) {
         return false;
       }
-      if (!!menuItem.offsetParent) {
+      if (menuItem.offsetParent) {
         return true;
       }
       // A "position: fixed" element won't have an offsetParent, so we have to