exclude "@babel/helpers - .." from js/unknown-directive

Author: erik-krogh

javascript/ql/src/Expressions/UnknownDirective.ql

@@ -16,5 +16,7 @@ where
   // ignore ":" pseudo-directive sometimes seen in dual-use shell/node.js scripts
   not d.getExpr().getStringValue() = ":" and
   // but exclude attribute top-levels: `<a href="javascript:'some-attribute-string'">`
-  not d.getParent() instanceof CodeInAttribute
+  not d.getParent() instanceof CodeInAttribute and
+  // exclude babel generated directives like "@babel/helpers - typeof". 
+  not d.getDirectiveText().prefix(14) = "@babel/helpers"
 select d, "Unknown directive: '" + truncate(d.getDirectiveText(), 20, " ... (truncated)") + "'."