Implementation.

index.js

@@ -0,0 +1,27 @@
+'use strict';
+
+var toStr = Object.prototype.toString;
+var hasSymbols = typeof Symbol === 'function' && typeof Symbol() === 'symbol';
+
+if (hasSymbols) {
+	var symToStr = Symbol.prototype.toString;
+	var symStringRegex = /^Symbol\(.*\)$/;
+	var isSymbolObject = function isSymbolObject(value) {
+		if (typeof value.valueOf() !== 'symbol') { return false; }
+		return symStringRegex.test(symToStr.call(value));
+	};
+	module.exports = function isSymbol(value) {
+		if (typeof value === 'symbol') { return true; }
+		if (toStr.call(value) !== '[object Symbol]') { return false; }
+		try {
+			return isSymbolObject(value);
+		} catch (e) {
+			return false;
+		}
+	};
+} else {
+	module.exports = function isSymbol(value) {
+		// this environment does not support Symbols.
+		return false;
+	};
+}