function wrap( idx ) {
	if ( !isNonNegativeInteger( idx ) ) {
		throw new TypeError( format( 'invalid argument. Must provide a nonnegative integer. Value: `%s`.', idx ) );
	}
	return argn;

	/**
	* Argument function.
	*
	* @private
	* @returns {*} argument
	*/
	function argn() {
		return arguments[ idx ];
	}
}
Returns a function which always returns a specified argument.

@param {NonNegativeInteger} idx - argument index
@throws {TypeError} must provide a nonnegative integer
@returns {Function} argument function

@example
var argn = wrap( 1 );

var v = argn( 1.0, 2.0, 3.0 );
// returns 2.0

v = argn( 'a', 'b', 'c' );
// returns 'b'

v = argn( null );
// returns undefined