index.js

'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;
	};
}