Improve code quality and write tests

node_modules/@babel/preset-env/data/shipped-proposals.js

@@ -0,0 +1,14 @@
+// These mappings represent the syntax proposals that have been
+// shipped by browsers, and are enabled by the `shippedProposals` option.
+
+const proposalPlugins = {};
+
+const pluginSyntaxMap = new Map([
+  ["proposal-async-generator-functions", "syntax-async-generators"],
+  ["proposal-object-rest-spread", "syntax-object-rest-spread"],
+  ["proposal-optional-catch-binding", "syntax-optional-catch-binding"],
+  ["proposal-unicode-property-regex", null],
+  ["proposal-json-strings", "syntax-json-strings"],
+]);
+
+module.exports = { proposalPlugins, pluginSyntaxMap };