fix: forbid access to object prototype props in mml parser (#43)

Author: kdegaltseva

src/parser/parser.test.tsx

@@ -98,3 +98,9 @@ test('invalid MML', () => {
   const mml = '<input name="test" value=1 />';
   expect(() => SourceToXML(mml)).toThrowError(/Attribute value expected/);
 });
+
+test('forbid access to object prototype props in mml', () => {
+  const mml = '<constructor />';
+  const nodes = SourceToXML(mml);
+  expect(() => XMLtoMMLTree(nodes)).toThrowError(/Converter not found for tag constructor.+/);
+});

src/parser/tree.ts

@@ -36,7 +36,7 @@ export class Tree {
 
     (parent.children || []).forEach((child, i) => {
       const converter = this.converters[child.name];
-      if (!converter) {
+      if (!converter || !Object.hasOwnProperty.call(this.converters, child.name)) {
         throw Error(
           `Converter not found for tag ${child.name}, Available converters are ${Object.keys(this.converters)}`,
         );