function isFunction( value ) {
	// Note: cannot use `typeof` directly, as various browser engines incorrectly return `'function'` when operating on non-function objects, such as regular expressions and NodeLists.
	return ( typeOf( value ) === 'function' );
}
Tests if a value is a function.

@param {*} value - value to test
@returns {boolean} boolean indicating whether value is a function

@example
function beep() {
    return 'beep';
}

var bool = isFunction( beep );
// returns true