--- /dev/null
+module.exports = isFunction
+
+var toString = Object.prototype.toString
+
+function isFunction (fn) {
+ var string = toString.call(fn)
+ return string === '[object Function]' ||
+ (typeof fn === 'function' && string !== '[object RegExp]') ||
+ (typeof window !== 'undefined' &&
+ // IE8 and below
+ (fn === window.setTimeout ||
+ fn === window.alert ||
+ fn === window.confirm ||
+ fn === window.prompt))
+};