function factory( fcns, clbk, thisArg ) {
	if ( !isFunctionArray( fcns ) ) {
		throw new TypeError( format( 'invalid argument. First argument must be an array of functions. Value: `%s`.', fcns ) );
	}
	if ( !isFunction( clbk ) ) {
		throw new TypeError( format( 'invalid argument. Second argument must be a function. Value: `%s`.', clbk ) );
	}
	return waterfall;

	/**
	* Executes functions in series, passing the results of one function as arguments to the next function.
	*
	* @private
	*/
	function waterfall() {
		var idx = -1;
		next(); // eslint-disable-line node/callback-return

		/**
		* Executes the next function in the series.
		*
		* @private
		* @param {(Error|null)} error - error object
		* @param {...*} args - results to pass to next callback
		* @returns {void}
		*/
		function next() {
			var args;
			var len;
			var i;

			// Check for an error...
			if ( arguments[ 0 ] ) {
				return clbk( arguments[ 0 ] );
			}
			// Update the counter and check if we have run all functions...
			idx += 1;
			if ( idx >= fcns.length ) {
				return clbk();
			}
			// Copy the remaining arguments...
			len = arguments.length;
			args = new Array( len );
			for ( i = 0; i < len-1; i++ ) {
				args[ i ] = arguments[ i+1 ];
			}
			// Add the callback:
			args[ i ] = next;

			// Apply the arguments to the next function in the waterfall:
			fcns[ idx ].apply( thisArg, args );
		}
	}
}
Returns a reusable waterfall function.

@param {FunctionArray} fcns - array of functions
@param {Callback} clbk - callback to invoke upon completion
@param {*} [thisArg] - function context
@throws {TypeError} first argument must be an array of functions
@throws {TypeError} second argument must be a function
@returns {Function} waterfall function

@example
function foo( next ) {
    next( null, 'beep' );
}

function bar( str, next ) {
    console.log( str );
    // => 'beep'

    next();
}

function done( error ) {
    if ( error ) {
        throw error;
    }
}

var fcns = [ foo, bar ];

var waterfall = factory( fcns, done );

waterfall();
waterfall();
waterfall();