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* @license Apache-2.0
*
* Copyright (c) 2018 The Stdlib Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
'use strict';
// MODULES //
var isFunctionArray = require( '@stdlib/assert/is-function-array' );
var isFunction = require( '@stdlib/assert/is-function' );
var format = require( '@stdlib/string/format' );
// MAIN //
/**
* 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();
*/
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 );
}
}
}
// EXPORTS //
module.exports = factory;
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