a === b -> identical(a, b)

runtime/lib/double.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 class _Double implements double {
   factory _Double.fromInteger(int value)
       native "Double_doubleFromInteger";
   int get hashCode {
     try {
       return toInt();
@@ skipping 139 matching lines @@
   String _toStringAsFixed(int fractionDigits) native "Double_toStringAsFixed";
 
   String toStringAsExponential(int fractionDigits) {
     // See ECMAScript-262, 15.7.4.6 for details.
 
     // The EcmaScript specification checks for NaN and Infinity before looking
     // at the fractionDigits. In Dart we are consistent with toStringAsFixed and
     // look at the fractionDigits first.
 
     // Step 7.
-    if (fractionDigits !== null &&
+    if (fractionDigits != null &&
         (fractionDigits < 0 || fractionDigits > 20)) {
       // TODO(antonm): should be proper RangeError or Dart counterpart.
       throw "Range error";
     }
 
     if (isNaN) return "NaN";
     if (this == double.INFINITY) return "Infinity";
     if (this == -double.INFINITY) return "-Infinity";
 
     // The dart function prints the shortest representation when fractionDigits
     // equals null. The native function wants -1 instead.
-    fractionDigits = (fractionDigits === null) ? -1 : fractionDigits;
+    fractionDigits = (fractionDigits == null) ? -1 : fractionDigits;
 
     return _toStringAsExponential(fractionDigits);
   }
   String _toStringAsExponential(int fractionDigits)
       native "Double_toStringAsExponential";
 
   String toStringAsPrecision(int precision) {
     // See ECMAScript-262, 15.7.4.7 for details.
 
     // The EcmaScript specification checks for NaN and Infinity before looking
@@ skipping 38 matching lines @@
         return EQUAL;
       }
     } else if (isNaN) {
       return other.isNaN ? EQUAL : GREATER;
     } else {
       // Other is NaN.
       return LESS;
     }
   }
 }