Implementation.

index.js

@@ -0,0 +1,36 @@
+'use strict';
+
+var flagsGetter = function flags() {
+	var str = String(this);
+	return str.slice(str.lastIndexOf('/') + 1);
+};
+
+var supportsDescriptors = (function () {
+	if (!Object.defineProperty) {
+		return false;
+	}
+	try {
+		Object.defineProperty({}, 'x', {});
+		return true;
+	} catch (e) { /* this is IE 8. */
+		return false;
+	}
+}());
+
+var flags = Function.call.bind(flagsGetter);
+
+flags.shim = function flagsShim() {
+	if (!supportsDescriptors) {
+		throw new TypeError('RegExp.prototype.flags requires a true ES5 environment that supports property descriptors');
+	}
+	if (/a/mig.flags !== 'gim') {
+		Object.defineProperty(RegExp.prototype, 'flags', {
+			configurable: true,
+			enumerable: false,
+			get: flagsGetter
+		});
+	}
+	return flags;
+};
+
+module.exports = flags;