fix: checks validity of an identifier

lib/utils/ast-utils.js

@@ -1,4 +1,5 @@
 const hashtable = require("./hashtable");
+const generateIdentifierRegex = require("./generateIdentifierRegex");
 
 function safeTraverse(obj, paths) {
 	let val = obj;
@@ -149,8 +150,8 @@ function createIdentifierOrLiteral(j, val) {
 			return createExternalRegExp(j, val);
 		} else {
 			// Use identifier instead
-			// TODO: Check if literalVal is a valid Identifier!
-			return j.identifier(literalVal);
+			if (!literalVal.match(generateIdentifierRegex()))
+				return j.identifier(literalVal);
 		}
 	}
 	return j.literal(literalVal);

lib/utils/generateIdentifierRegex.js

@@ -0,0 +1,55 @@
+const regenerate = require("regenerate");
+const template = require("lodash/template");
+
+// Which Unicode version should be used?
+const UNICODE_VERSION = "10.0.0";
+
+// Set up a shorthand function to import Unicode data.
+const get = function(what) {
+	return require(`unicode-${ UNICODE_VERSION }/${ what }/code-points.js`);
+};
+
+// Get the Unicode properties needed to construct the ES6 regex.
+const idStart = get("Binary_Property/ID_Start");
+const idContinue = get("Binary_Property/ID_Continue");
+const otherIdStart = get("Binary_Property/Other_ID_Start");
+
+const compileRegex = template("/^(?!(?:<%= reservedWords %>)$)" +
+	"(?:<%= identifierStart %>)(?:<%= identifierPart %>)*$/");
+
+module.exports = function generateES6Regex() {
+	const identifierStart = regenerate(idStart)
+		.add(
+			"$",
+			"_"
+		);
+	const identifierPart = regenerate(idContinue)
+		.add(otherIdStart)
+		.add(
+			"$",
+			"_",
+			"\u200C",
+			"\u200D"
+		);
+
+	const reservedWords = [
+		// https://mathiasbynens.be/notes/reserved-keywords#ecmascript-6
+		"do", "if", "in", "for", "let", "new", "try", "var", "case", "else",
+		"enum", "eval", "null", "this", "true", "void", "with", "await", "break",
+		"catch", "class", "const", "false", "super", "throw", "while", "yield",
+		"delete", "export", "import", "public", "return", "static", "switch",
+		"typeof", "default", "extends", "finally", "package", "private",
+		"continue", "debugger", "function", "arguments", "interface", "protected",
+		"implements", "instanceof",
+		// These aren’t strictly reserved words, but they kind of behave as if
+		// they were.
+		//'NaN', 'Infinity', 'undefined'
+	];
+
+	const regex = compileRegex({
+		reservedWords: reservedWords.join("|"),
+		identifierStart: identifierStart.toString(),
+		identifierPart: identifierPart.toString()
+	});
+	return regex;
+};

package.json

@@ -100,6 +100,7 @@
     "p-each-series": "^1.0.0",
     "p-lazy": "^1.0.0",
     "prettier": "^1.5.3",
+    "regenerate": "^1.3.3",
     "resolve-cwd": "^2.0.0",
     "supports-color": "^5.3.0",
     "v8-compile-cache": "^1.1.2",
@@ -131,6 +132,7 @@
     "nyc": "^11.6.0",
     "prettier-eslint-cli": "^4.7.1",
     "schema-utils": "^0.4.5",
+    "unicode-10.0.0": "^0.7.5",
     "webpack": "^4.2.0",
     "webpack-dev-server": "^3.0.0"
   },