function createClass( ctor ) {
	var str = '';
	if ( !ctor ) {
		ctor = 'Float64Array';
	}
	str += '(function create() {';
	str += 'class CustomTypedArray extends '+ctor+' {';
	str += 'constructor( data ) {';
	str += 'super( data );';
	str += '}';
	str += '}';
	str += 'return CustomTypedArray;';
	str += '})()';
	return eval( str ); // eslint-disable-line no-eval
}
Creates a CustomTypedArray class constructor. Note that we use function generation so that tests may be run in browsers not supporting ES2015 classes. This function may be loaded in non-ES2015 environments, but should only be invoked when ES2015 classes are supported.

@private
@param {string} ctor - typed array constructor name
@returns {Function} constructor