diff --git a/sdk/lib/_internal/js_dev_runtime/private/foreign_helper.dart b/sdk/lib/_internal/js_dev_runtime/private/foreign_helper.dart
index 02e5c24cd99..588d789c231 100644
--- a/sdk/lib/_internal/js_dev_runtime/private/foreign_helper.dart
+++ b/sdk/lib/_internal/js_dev_runtime/private/foreign_helper.dart
@@ -106,10 +106,7 @@ library dart._foreign_helper;
  */
 // Add additional optional arguments if needed. The method is treated internally
 // as a variable argument method.
-// TODO(vsm): Enforce that this doesn't fall back to dynamic by typing it as:
-//  `T JS<T extends Object>(...)`
-// once we clean up html libraries.
-T JS<T>(String typeDescription, String codeTemplate,
+T JS<T extends Object>(String typeDescription, String codeTemplate,
     [arg0,
     arg1,
     arg2,
diff --git a/sdk/lib/html/dart2js/html_dart2js.dart b/sdk/lib/html/dart2js/html_dart2js.dart
index 5de4de4425e..8dc677d4ee4 100644
--- a/sdk/lib/html/dart2js/html_dart2js.dart
+++ b/sdk/lib/html/dart2js/html_dart2js.dart
@@ -13273,28 +13273,28 @@ class Element extends Node
 
   final Element offsetParent;
 
-  int get offsetHeight => JS('num', '#.offsetHeight', this).round();
+  int get offsetHeight => JS<num>('num', '#.offsetHeight', this).round();
 
-  int get offsetLeft => JS('num', '#.offsetLeft', this).round();
+  int get offsetLeft => JS<num>('num', '#.offsetLeft', this).round();
 
-  int get offsetTop => JS('num', '#.offsetTop', this).round();
+  int get offsetTop => JS<num>('num', '#.offsetTop', this).round();
 
-  int get offsetWidth => JS('num', '#.offsetWidth', this).round();
+  int get offsetWidth => JS<num>('num', '#.offsetWidth', this).round();
 
-  int get scrollHeight => JS('num', '#.scrollHeight', this).round();
-  int get scrollLeft => JS('num', '#.scrollLeft', this).round();
+  int get scrollHeight => JS<num>('num', '#.scrollHeight', this).round();
+  int get scrollLeft => JS<num>('num', '#.scrollLeft', this).round();
 
   set scrollLeft(int value) {
     JS("void", "#.scrollLeft = #", this, value.round());
   }
 
-  int get scrollTop => JS('num', '#.scrollTop', this).round();
+  int get scrollTop => JS<num>('num', '#.scrollTop', this).round();
 
   set scrollTop(int value) {
     JS("void", "#.scrollTop = #", this, value.round());
   }
 
-  int get scrollWidth => JS('num', '#.scrollWidth', this).round();
+  int get scrollWidth => JS<num>('num', '#.scrollWidth', this).round();
 
   // To suppress missing implicit constructor warnings.
   factory Element._() {
@@ -28848,14 +28848,14 @@ class Touch extends Interceptor {
 
 // As of Chrome 37, these all changed from long to double.  This code
 // preserves backwards compatibility for the time being.
-  int get __clientX => JS('num', '#.clientX', this).round();
-  int get __clientY => JS('num', '#.clientY', this).round();
-  int get __screenX => JS('num', '#.screenX', this).round();
-  int get __screenY => JS('num', '#.screenY', this).round();
-  int get __pageX => JS('num', '#.pageX', this).round();
-  int get __pageY => JS('num', '#.pageY', this).round();
-  int get __radiusX => JS('num', '#.radiusX', this).round();
-  int get __radiusY => JS('num', '#.radiusY', this).round();
+  int get __clientX => JS<num>('num', '#.clientX', this).round();
+  int get __clientY => JS<num>('num', '#.clientY', this).round();
+  int get __screenX => JS<num>('num', '#.screenX', this).round();
+  int get __screenY => JS<num>('num', '#.screenY', this).round();
+  int get __pageX => JS<num>('num', '#.pageX', this).round();
+  int get __pageY => JS<num>('num', '#.pageY', this).round();
+  int get __radiusX => JS<num>('num', '#.radiusX', this).round();
+  int get __radiusY => JS<num>('num', '#.radiusY', this).round();
 
   Point get client => new Point(__clientX, __clientY);
 
@@ -30617,8 +30617,11 @@ class Window extends EventTarget
   void _cancelAnimationFrame(int id) native;
 
   _ensureRequestAnimationFrame() {
-    if (JS('bool', '!!(#.requestAnimationFrame && #.cancelAnimationFrame)',
-        this, this)) return;
+    if (JS<bool>(
+        'bool',
+        '!!(#.requestAnimationFrame && #.cancelAnimationFrame)',
+        this,
+        this)) return;
 
     JS(
         'void',
@@ -32110,9 +32113,9 @@ class Window extends EventTarget
     return db;
   }
 
-  int get pageXOffset => JS('num', '#.pageXOffset', this).round();
+  int get pageXOffset => JS<num>('num', '#.pageXOffset', this).round();
 
-  int get pageYOffset => JS('num', '#.pageYOffset', this).round();
+  int get pageYOffset => JS<num>('num', '#.pageYOffset', this).round();
 
   /**
    * The distance this window has been scrolled horizontally.
@@ -32124,8 +32127,8 @@ class Window extends EventTarget
    * * [scrollX](https://developer.mozilla.org/en-US/docs/Web/API/Window.scrollX)
    *   from MDN.
    */
-  int get scrollX => JS('bool', '("scrollX" in #)', this)
-      ? JS('num', '#.scrollX', this).round()
+  int get scrollX => JS<bool>('bool', '("scrollX" in #)', this)
+      ? JS<num>('num', '#.scrollX', this).round()
       : document.documentElement.scrollLeft;
 
   /**
@@ -32138,8 +32141,8 @@ class Window extends EventTarget
    * * [scrollY](https://developer.mozilla.org/en-US/docs/Web/API/Window.scrollY)
    *   from MDN.
    */
-  int get scrollY => JS('bool', '("scrollY" in #)', this)
-      ? JS('num', '#.scrollY', this).round()
+  int get scrollY => JS<bool>('bool', '("scrollY" in #)', this)
+      ? JS<num>('num', '#.scrollY', this).round()
       : document.documentElement.scrollTop;
 }
 
@@ -32154,7 +32157,7 @@ class _BeforeUnloadEvent extends _WrappedEvent implements BeforeUnloadEvent {
     _returnValue = value;
     // FF and IE use the value as the return value, Chrome will return this from
     // the event callback function.
-    if (JS('bool', '("returnValue" in #)', wrapped)) {
+    if (JS<bool>('bool', '("returnValue" in #)', wrapped)) {
       JS('void', '#.returnValue = #', wrapped, value);
     }
   }
diff --git a/sdk/lib/html/html_common/conversions.dart b/sdk/lib/html/html_common/conversions.dart
index f2373b50d90..a563c050798 100644
--- a/sdk/lib/html/html_common/conversions.dart
+++ b/sdk/lib/html/html_common/conversions.dart
@@ -237,9 +237,9 @@ abstract class _AcceptStructuredClone {
     }
 
     if (isJavaScriptArray(e)) {
-      var l = JS('returns:List;creates:;', '#', e);
+      var l = JS<List>('returns:List;creates:;', '#', e);
       var slot = findSlot(l);
-      var copy = JS('returns:List|Null;creates:;', '#', readSlot(slot));
+      var copy = JS<List>('returns:List|Null;creates:;', '#', readSlot(slot));
       if (copy != null) return copy;
 
       int length = l.length;
diff --git a/tests/compiler/dart2js/analyses/api_allowed.json b/tests/compiler/dart2js/analyses/api_allowed.json
index a97e98f44ef..9a02f59ef79 100644
--- a/tests/compiler/dart2js/analyses/api_allowed.json
+++ b/tests/compiler/dart2js/analyses/api_allowed.json
@@ -87,7 +87,6 @@
     "Dynamic access of 'firstChild'.": 2,
     "Dynamic invocation of 'append'.": 1,
     "Dynamic access of 'tagName'.": 2,
-    "Dynamic invocation of 'round'.": 20,
     "Dynamic invocation of 'call'.": 1,
     "Dynamic invocation of 'dart.dom.html::_initKeyboardEvent'.": 1,
     "Dynamic access of 'attributes'.": 1,
@@ -99,9 +98,7 @@
     "Dynamic invocation of 'createElement'.": 1
   },
   "org-dartlang-sdk:///sdk/lib/html/html_common/conversions.dart": {
-    "Dynamic invocation of '[]='.": 2,
-    "Dynamic access of 'length'.": 1,
-    "Dynamic invocation of '[]'.": 1
+    "Dynamic invocation of '[]='.": 1
   },
   "org-dartlang-sdk:///sdk/lib/html/html_common/filtered_element_list.dart": {
     "Dynamic invocation of 'remove'.": 1
diff --git a/tools/dom/templates/html/impl/impl_Element.darttemplate b/tools/dom/templates/html/impl/impl_Element.darttemplate
index 2786eee3696..8783228c015 100644
--- a/tools/dom/templates/html/impl/impl_Element.darttemplate
+++ b/tools/dom/templates/html/impl/impl_Element.darttemplate
@@ -1492,28 +1492,28 @@ $(ANNOTATIONS)$(NATIVESPEC)class $CLASSNAME$EXTENDS$IMPLEMENTS {
 
   final Element offsetParent;
 
-  int get offsetHeight => JS('num', '#.offsetHeight', this).round();
+  int get offsetHeight => JS<num>('num', '#.offsetHeight', this).round();
 
-  int get offsetLeft => JS('num', '#.offsetLeft', this).round();
+  int get offsetLeft => JS<num>('num', '#.offsetLeft', this).round();
 
-  int get offsetTop => JS('num', '#.offsetTop', this).round();
+  int get offsetTop => JS<num>('num', '#.offsetTop', this).round();
 
-  int get offsetWidth => JS('num', '#.offsetWidth', this).round();
+  int get offsetWidth => JS<num>('num', '#.offsetWidth', this).round();
 
-  int get scrollHeight => JS('num', '#.scrollHeight', this).round();
-  int get scrollLeft => JS('num', '#.scrollLeft', this).round();
+  int get scrollHeight => JS<num>('num', '#.scrollHeight', this).round();
+  int get scrollLeft => JS<num>('num', '#.scrollLeft', this).round();
 
   set scrollLeft(int value) {
     JS("void", "#.scrollLeft = #", this, value.round());
   }
 
-  int get scrollTop => JS('num', '#.scrollTop', this).round();
+  int get scrollTop => JS<num>('num', '#.scrollTop', this).round();
 
   set scrollTop(int value) {
     JS("void", "#.scrollTop = #", this, value.round());
   }
 
-  int get scrollWidth => JS('num', '#.scrollWidth', this).round();
+  int get scrollWidth => JS<num>('num', '#.scrollWidth', this).round();
 
 $!MEMBERS
 }
diff --git a/tools/dom/templates/html/impl/impl_Touch.darttemplate b/tools/dom/templates/html/impl/impl_Touch.darttemplate
index ef3b5c29a03..2d84399b62d 100644
--- a/tools/dom/templates/html/impl/impl_Touch.darttemplate
+++ b/tools/dom/templates/html/impl/impl_Touch.darttemplate
@@ -9,14 +9,14 @@ $!MEMBERS
 
 // As of Chrome 37, these all changed from long to double.  This code
 // preserves backwards compatibility for the time being.
-  int get __clientX => JS('num', '#.clientX', this).round();
-  int get __clientY => JS('num', '#.clientY', this).round();
-  int get __screenX => JS('num', '#.screenX', this).round();
-  int get __screenY => JS('num', '#.screenY', this).round();
-  int get __pageX => JS('num', '#.pageX', this).round();
-  int get __pageY => JS('num', '#.pageY', this).round();
-  int get __radiusX => JS('num', '#.radiusX', this).round();
-  int get __radiusY => JS('num', '#.radiusY', this).round();
+  int get __clientX => JS<num>('num', '#.clientX', this).round();
+  int get __clientY => JS<num>('num', '#.clientY', this).round();
+  int get __screenX => JS<num>('num', '#.screenX', this).round();
+  int get __screenY => JS<num>('num', '#.screenY', this).round();
+  int get __pageX => JS<num>('num', '#.pageX', this).round();
+  int get __pageY => JS<num>('num', '#.pageY', this).round();
+  int get __radiusX => JS<num>('num', '#.radiusX', this).round();
+  int get __radiusY => JS<num>('num', '#.radiusY', this).round();
 
   Point get client => new Point(__clientX, __clientY);
 
diff --git a/tools/dom/templates/html/impl/impl_Window.darttemplate b/tools/dom/templates/html/impl/impl_Window.darttemplate
index ec7d83cbea8..9553f4a3d2d 100644
--- a/tools/dom/templates/html/impl/impl_Window.darttemplate
+++ b/tools/dom/templates/html/impl/impl_Window.darttemplate
@@ -129,7 +129,7 @@ $(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS {
   void _cancelAnimationFrame(int id) native;
 
   _ensureRequestAnimationFrame() {
-    if (JS('bool',
+    if (JS<bool>('bool',
            '!!(#.requestAnimationFrame && #.cancelAnimationFrame)', this, this))
       return;
 
@@ -241,9 +241,9 @@ $!MEMBERS
     return db;
   }
 
-  int get pageXOffset => JS('num', '#.pageXOffset', this).round();
+  int get pageXOffset => JS<num>('num', '#.pageXOffset', this).round();
 
-  int get pageYOffset => JS('num', '#.pageYOffset', this).round();
+  int get pageYOffset => JS<num>('num', '#.pageYOffset', this).round();
 
   /**
    * The distance this window has been scrolled horizontally.
@@ -255,8 +255,8 @@ $!MEMBERS
    * * [scrollX](https://developer.mozilla.org/en-US/docs/Web/API/Window.scrollX)
    *   from MDN.
    */
-  int get scrollX => JS('bool', '("scrollX" in #)', this) ?
-      JS('num', '#.scrollX', this).round() :
+  int get scrollX => JS<bool>('bool', '("scrollX" in #)', this) ?
+      JS<num>('num', '#.scrollX', this).round() :
       document.documentElement.scrollLeft;
 
   /**
@@ -269,8 +269,8 @@ $!MEMBERS
    * * [scrollY](https://developer.mozilla.org/en-US/docs/Web/API/Window.scrollY)
    *   from MDN.
    */
-  int get scrollY => JS('bool', '("scrollY" in #)', this) ?
-      JS('num', '#.scrollY', this).round() :
+  int get scrollY => JS<bool>('bool', '("scrollY" in #)', this) ?
+      JS<num>('num', '#.scrollY', this).round() :
       document.documentElement.scrollTop;
 }
 
@@ -285,7 +285,7 @@ class _BeforeUnloadEvent extends _WrappedEvent implements BeforeUnloadEvent {
     _returnValue = value;
     // FF and IE use the value as the return value, Chrome will return this from
     // the event callback function.
-    if (JS('bool', '("returnValue" in #)', wrapped)) {
+    if (JS<bool>('bool', '("returnValue" in #)', wrapped)) {
       JS('void', '#.returnValue = #', wrapped, value);
     }
   }