Improve code quality and write tests

node_modules/@babel/preset-env/lib/polyfills/regenerator/entry-plugin.js

@@ -0,0 +1,48 @@
+"use strict";
+
+Object.defineProperty(exports, "__esModule", {
+  value: true
+});
+exports.default = _default;
+
+var _utils = require("../../utils");
+
+function isRegeneratorSource(source) {
+  return source === "regenerator-runtime/runtime";
+}
+
+function _default() {
+  const visitor = {
+    ImportDeclaration(path) {
+      if (isRegeneratorSource((0, _utils.getImportSource)(path))) {
+        this.regeneratorImportExcluded = true;
+        path.remove();
+      }
+    },
+
+    Program(path) {
+      path.get("body").forEach(bodyPath => {
+        if (isRegeneratorSource((0, _utils.getRequireSource)(bodyPath))) {
+          this.regeneratorImportExcluded = true;
+          bodyPath.remove();
+        }
+      });
+    }
+
+  };
+  return {
+    name: "regenerator-entry",
+    visitor,
+
+    pre() {
+      this.regeneratorImportExcluded = false;
+    },
+
+    post() {
+      if (this.opts.debug && this.regeneratorImportExcluded) {
+        console.log(`\n[${this.file.opts.filename}] Based on your targets, regenerator-runtime import excluded.`);
+      }
+    }
+
+  };
+}

node_modules/@babel/preset-env/lib/polyfills/regenerator/usage-plugin.js

@@ -0,0 +1,39 @@
+"use strict";
+
+Object.defineProperty(exports, "__esModule", {
+  value: true
+});
+exports.default = _default;
+
+var _utils = require("../../utils");
+
+function _default() {
+  return {
+    name: "regenerator-usage",
+
+    pre() {
+      this.usesRegenerator = false;
+    },
+
+    visitor: {
+      Function(path) {
+        const {
+          node
+        } = path;
+
+        if (!this.usesRegenerator && (node.generator || node.async)) {
+          this.usesRegenerator = true;
+          (0, _utils.createImport)(path, "regenerator-runtime");
+        }
+      }
+
+    },
+
+    post() {
+      if (this.opts.debug && this.usesRegenerator) {
+        console.log(`\n[${this.file.opts.filename}] Based on your code and targets, added regenerator-runtime.`);
+      }
+    }
+
+  };
+}