A dart int literal is a dart2js' int unless it will become NaN or infinity.

sdk/lib/_internal/compiler/implementation/js_backend/constant_system_javascript.dart

Index: sdk/lib/_internal/compiler/implementation/js_backend/constant_system_javascript.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/js_backend/constant_system_javascript.dart	(revision 25000)
+++ sdk/lib/_internal/compiler/implementation/js_backend/constant_system_javascript.dart	(working copy)
@@ -177,6 +177,16 @@
   const JavaScriptConstantSystem();
 
   /**
+   * Returns true if the given [value] will turn into NaN or infinity

[karlklose, 2013/07/15 13:52:08]

'... true if [value] will...'?

[ngeoffray, 2013/07/15 13:53:38]

Done.

+   * at runtime.
+   */
+  bool integerBecomesNanOrInfinity(int value) {
+    int absValue = value.abs();

[floitsch, 2013/07/15 13:25:51]

Why do you need the absolute value? isNaN and isInfinite should work on the
negative value too.

[ngeoffray, 2013/07/15 13:49:27]

Done.

+    double doubleValue = absValue.toDouble();
+    return doubleValue.isNaN || doubleValue.isInfinite;
+  }
+
+  /**
    * Returns true if the given [value] fits into a double without losing
    * precision.
    */
@@ -187,13 +197,20 @@
     return value.toDouble().floor().toInt() == value;
   }
 
+

[karlklose, 2013/07/15 13:52:08]

Remove extra line.

[ngeoffray, 2013/07/15 13:53:38]

Done.

   NumConstant convertToJavaScriptConstant(NumConstant constant) {
     if (constant.isInt()) {
       IntConstant intConstant = constant;
       int intValue = intConstant.value;
-      if (!integerFitsIntoDouble(intValue)) {
+      if (integerBecomesNanOrInfinity(intValue)) {
         return new DoubleConstant(intValue.toDouble());
       }
+      // If the integer looses precision with JavaScript numbers, use

[karlklose, 2013/07/15 13:52:08]

'looses' -> 'loses'.

[ngeoffray, 2013/07/15 13:53:38]

Done.

+      // the floored version JavaScript will use.
+      int floorValue = intValue.toDouble().floor().toInt();
+      if (floorValue != intValue) {
+        return new IntConstant(floorValue);
+      }
     } else if (constant.isDouble()) {
       DoubleConstant doubleResult = constant;
       double doubleValue = doubleResult.value;