Improve code quality and write tests

node_modules/regexp-tree/dist/interpreter/finite-automaton/transforms/char-plus-to-star-transform.js

@@ -0,0 +1,35 @@
+/**
+ * The MIT License (MIT)
+ * Copyright (c) 2017-present Dmitry Soshnikov <dmitry.soshnikov@gmail.com>
+ */
+
+'use strict';
+
+/**
+ * A regexp-tree plugin to replace `a+` to `aa*`, since NFA/DFA
+ * handles Kleene-closure `a*`, and `a+` is just a syntactic sugar.
+ */
+
+module.exports = {
+  Repetition: function Repetition(path) {
+    var node = path.node,
+        parent = path.parent;
+
+
+    if (node.quantifier.kind !== '+') {
+      return;
+    }
+
+    if (parent.type === 'Alternative') {
+      path.getParent().insertChildAt(node.expression, path.index);
+    } else {
+      path.replace({
+        type: 'Alternative',
+        expressions: [node.expression, node]
+      });
+    }
+
+    // Change quantifier.
+    node.quantifier.kind = '*';
+  }
+};

node_modules/regexp-tree/dist/interpreter/finite-automaton/transforms/index.js

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+/**
+ * The MIT License (MIT)
+ * Copyright (c) 2017-present Dmitry Soshnikov <dmitry.soshnikov@gmail.com>
+ */
+
+'use strict';
+
+module.exports = [
+// a+ -> aa*
+require('./char-plus-to-star-transform')];