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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 isFunction = require( '@stdlib/assert/is-function' );
var isCollection = require( '@stdlib/assert/is-collection' );
var format = require( '@stdlib/string/format' );
var PINF = require( '@stdlib/constants/float64/pinf' );
var validate = require( './validate.js' );
var limit = require( './limit.js' );
// MAIN //
/**
* Returns a function to invoke a function once for each element in a collection.
*
* ## Notes
*
* - If a provided function calls the provided callback with a truthy error argument, the function suspends execution and immediately calls the `done` callback for subsequent error handling.
* - This function does **not** guarantee that execution is asynchronous. To do so, wrap the `done` callback in a function which either executes at the end of the current stack (e.g., `nextTick`) or during a subsequent turn of the event loop (e.g., `setImmediate`, `setTimeout`).
*
* @param {Options} [options] - function options
* @param {*} [options.thisArg] - execution context
* @param {PositiveInteger} [options.limit] - maximum number of pending invocations at any one time
* @param {boolean} [options.series=false] - boolean indicating whether to wait for a previous invocation to complete before invoking a provided function for the next element in a collection
* @param {Function} fcn - function to invoke for each element in a collection
* @throws {TypeError} options argument must be an object
* @throws {TypeError} must provide valid options
* @throws {TypeError} last argument must be a function
* @returns {Function} function which invokes the provided function once for each element in a collection
*
* @example
* var readFile = require( '@stdlib/fs/read-file' );
*
* function read( file, next ) {
* var opts = {
* 'encoding': 'utf8'
* };
* readFile( file, opts, onFile );
*
* function onFile( error ) {
* if ( error ) {
* return next( error );
* }
* console.log( 'Successfully read file: %s', file );
* next();
* }
* }
*
* var opts = {
* 'series': true
* };
*
* // Create a `forEachAsync` function which invokes `read` for each collection element sequentially:
* var forEachAsync = factory( opts, read );
*
* // Create a collection over which to iterate:
* var files = [
* './beep.js',
* './boop.js'
* ];
*
* // Define a callback which handles errors:
* function done( error ) {
* if ( error ) {
* console.error( error.message );
* return;
* }
* console.log( 'Successfully read all files.' );
* }
*
* // Run `read` for each element in `files`:
* forEachAsync( files, done );
*/
function factory( options, fcn ) {
var opts;
var err;
var f;
opts = {};
if ( arguments.length > 1 ) {
err = validate( opts, options );
if ( err ) {
throw err;
}
f = fcn;
} else {
f = options;
}
if ( !isFunction( f ) ) {
throw new TypeError( format( 'invalid argument. Last argument must be a function. Value: `%', f ) );
}
if ( opts.series ) {
opts.limit = 1;
} else if ( !opts.limit ) {
opts.limit = PINF;
}
return forEachAsync;
/**
* Invokes a function for each element in a collection.
*
* @private
* @param {Collection} collection - input collection
* @param {Callback} done - function to invoke upon completion
* @throws {TypeError} first argument must be a collection
* @throws {TypeError} last argument must be a function
* @returns {Object} status object
*/
function forEachAsync( collection, done ) {
// Status object
var status = {
'status': 'pending',
'ndone': 0,
'nerrors': 0
};
if ( !isCollection( collection ) ) {
throw new TypeError( format( 'invalid argument. First argument must be a collection. Value: `%s`.', collection ) );
}
if ( !isFunction( done ) ) {
throw new TypeError( format( 'invalid argument. Last argument must be a function. Value: `%s`.', done ) );
}
/**
* Wrapper function to invoke the iterator.
*
* @private
* @param {*} value - iterated value
* @param {number} index - iteration index
* @param {Collection} collection - input collection
* @param {Function} next - callback to invoke after processing an element
*/
function wrapped( value, index, collection, next ) {
f.call( opts.thisArg, value, index, collection, onDone );
/**
* Callback invoked upon completion.
*
* @private
* @param {(Error|null)} error - error object
* @returns {void}
*/
function onDone( error ) {
if ( error ) {
status.nerrors += 1;
return next( error );
}
// Hook successful completion:
status.ndone += 1; // 'this' must be the returned function object
next();
}
}
limit( collection, opts, wrapped.bind(status), clbk );
return status;
/**
* Callback invoked upon completion.
*
* @private
* @param {*} [error] - error object
* @returns {void}
*/
function clbk( error ) {
if ( error ) {
status.status = 'fail';
return done( error );
}
status.status = 'ok';
done();
}
}
}
// EXPORTS //
module.exports = factory;
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