[strong] no sloppy equality

src/preparser.h

Index: src/preparser.h
diff --git a/src/preparser.h b/src/preparser.h
index 4b526f5f1f3c6f039ae730c70b07eccfa8a20444..33d87da6fb2128b4ad56e2bad445cd875d8d4df5 100644
--- a/src/preparser.h
+++ b/src/preparser.h
@@ -2445,6 +2445,7 @@ ParserBase<Traits>::ParseBinaryExpression(int prec, bool accept_IN, bool* ok) {
     // prec1 >= 4
     while (Precedence(peek(), accept_IN) == prec1) {
       Token::Value op = Next();
+      Scanner::Location op_location = scanner()->location();
       int pos = position();
       ExpressionT y = ParseBinaryExpression(prec1 + 1, accept_IN, CHECK_OK);
 
@@ -2464,6 +2465,11 @@ ParserBase<Traits>::ParseBinaryExpression(int prec, bool accept_IN, bool* ok) {
           case Token::NE_STRICT: cmp = Token::EQ_STRICT; break;
           default: break;
         }
+        if (cmp == Token::EQ && is_strong(language_mode())) {
+          ReportMessageAt(op_location, "strong_equal");
+          *ok = false;
+          return this->EmptyExpression();
+        }
         x = factory()->NewCompareOperation(cmp, x, y, pos);
         if (cmp != op) {
           // The comparison was negated - add a NOT.