Do not allow arrow functions in the middle of an expression

lib/parse.js

@@ -2477,6 +2477,16 @@ function parse($TEXT, options) {
             return arrow_function([]);
         }
 
+        if (is("name") && is_token(peek(), "arrow")) {
+            var param = new AST_SymbolFunarg({
+                name: start.value,
+                start: start,
+                end: start,
+            });
+            next();
+            return arrow_function([param])
+        }
+
         var left = maybe_conditional(no_in);
         var val = S.token.value;
 
@@ -2493,14 +2503,6 @@ function parse($TEXT, options) {
             }
             croak("SyntaxError: Invalid assignment");
         }
-        if (is("arrow")) {
-            left = new AST_SymbolFunarg({
-                name: left.name,
-                start: left.start,
-                end: left.end,
-            });
-            return arrow_function([left])
-        }
         return left;
     };