time-to-botec

README.md (10292B)

---

 <!--
 
 @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
 
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 distributed under the License is distributed on an "AS IS" BASIS,
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 See the License for the specific language governing permissions and
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 # reduceRightAsync
 
 > Apply a function against an accumulator and each element in a collection and return the accumulated result, iterating from right to left.
 
 <!-- Section to include introductory text. Make sure to keep an empty line after the intro `section` element and another before the `/section` close. -->
 
 <section class="intro">
 
 </section>
 
 <!-- /.intro -->
 
 <!-- Package usage documentation. -->
 
 <section class="usage">
 
 ## Usage
 
 ```javascript
 var reduceRightAsync = require( '@stdlib/utils/async/reduce-right' );
 ```
 
 #### reduceRightAsync( collection, initial, \[options,] reducer, done )
 
 Applies a `function` against an accumulator and each element in a `collection` and returns the accumulated result, iterating from right to left.
 
 ```javascript
 function reducer( acc, value, index, next ) {
     setTimeout( onTimeout, value );
     function onTimeout() {
         console.log( value );
         acc.sum += value;
         next( null, acc );
     }
 }
 
 function done( error, acc ) {
     if ( error ) {
         throw error;
     }
     console.log( acc.sum );
 }
 
 var arr = [ 1000, 2500, 3000 ];
 var acc = {
     'sum': 0
 };
 reduceRightAsync( arr, acc, reducer, done );
 /*
     3000
     2500
     1000
     6500
 */
 ```
 
 The `next` callback accepts two arguments: `error` and `accumulator`. The second argument to the `next` callback is passed as the first argument to the provided `reducer`.
 
 <!-- eslint-disable no-use-before-define -->
 
 ```javascript
 function reducer( acc, value, index, next ) {
     setTimeout( onTimeout, value );
     function onTimeout() {
         next( null, acc );
     }
 }
 
 function done( error, out ) {
     if ( error ) {
         throw error;
     }
     console.log( out === acc );
     // => true
 }
 
 var arr = [ 1000, 2500, 3000 ];
 var acc = {};
 
 reduceRightAsync( arr, acc, reducer, done );
 ```
 
 The function accepts the following `options`:
 
 -   `limit`: the maximum number of pending invocations at any one time. If provided, the function sets `options.series=false`. Default: `infinity`.
 -   `series`: `boolean` indicating whether to sequentially invoke `reducer` for each `collection` element. If `true`, the function sets `options.limit=1`. Default: `true`.
 -   `thisArg`: the execution context for `reducer`.
 
 By default, all elements are processed **sequentially**, which means that the function **does** guarantee completion order. To process each `collection` element concurrently, set the `series` option to `false`.
 
 ```javascript
 function reducer( acc, value, index, next ) {
     setTimeout( onTimeout, value );
     function onTimeout() {
         console.log( value );
         acc.sum += value;
         next( null, acc );
     }
 }
 
 function done( error, acc ) {
     if ( error ) {
         throw error;
     }
     console.log( acc.sum );
 }
 
 var arr = [ 1000, 2500, 3000 ];
 
 var acc = {
     'sum': 0
 };
 
 var opts = {
     'series': false
 };
 
 reduceRightAsync( arr, acc, opts, reducer, done );
 /* =>
     1000
     2500
     3000
     6500
 */
 ```
 
 To limit the maximum number of pending function invocations, set the `limit` option.
 
 ```javascript
 function reducer( acc, value, index, next ) {
     setTimeout( onTimeout, value );
     function onTimeout() {
         console.log( value );
         acc.sum += value;
         next( null, acc );
     }
 }
 
 function done( error, acc ) {
     if ( error ) {
         throw error;
     }
     console.log( acc.sum );
 }
 
 var arr = [ 1000, 2500, 3000 ];
 
 var acc = {
     'sum': 0
 };
 
 var opts = {
     'limit': 2
 };
 
 reduceRightAsync( arr, acc, opts, reducer, done );
 /* =>
     2500
     3000
     1000
     6500
 */
 ```
 
 To set the execution context of `reducer`, set the `thisArg` option.
 
 ```javascript
 function reducer( acc, value, index, next ) {
     this.count += 1;
     setTimeout( onTimeout, value );
     function onTimeout() {
         acc.sum += value;
         next( null, acc );
     }
 }
 
 var arr = [ 1000, 2500, 3000 ];
 
 var acc = {
     'sum': 0
 };
 
 var context = {
     'count': 0
 };
 
 var opts = {
     'thisArg': context
 };
 
 reduceRightAsync( arr, acc, opts, reducer, done );
 
 function done( error, acc ) {
     if ( error ) {
         throw error;
     }
     console.log( acc.sum );
     // => 6500
 
     console.log( context.count );
     // => 3
 }
 ```
 
 When invoked, `reducer` is provided a maximum of five arguments:
 
 -   `accumulator`: accumulated value.
 -   `value`: collection value.
 -   `index`: collection index.
 -   `collection`: the input `collection`.
 -   `next`: a callback which should be called once `reducer` has finished processing a collection `value`.
 
 The actual number of provided arguments depends on function `length`. If `reducer` accepts three arguments, `reducer` is provided `accumulator`, `value` and `next`. If `reducer` accepts four arguments, `reducer` is provided `accumulator`, `value`, `index`, and `next`. For every other `reducer` signature, `reducer` is provided all five arguments.
 
 ```javascript
 function reducer( acc, value, i, collection, next ) {
     console.log( 'collection: %s. %d: %d', collection.join( ',' ), i, value );
     setTimeout( onTimeout, value );
     function onTimeout() {
         console.log( value );
         acc.sum += value;
         next( null, acc );
     }
 }
 
 function done( error, acc ) {
     if ( error ) {
         throw error;
     }
     console.log( acc.sum );
 }
 
 var arr = [ 1000, 2500, 3000 ];
 
 var acc = {
     'sum': 0
 };
 
 reduceRightAsync( arr, acc, reducer, done );
 /* =>
     collection: 3000,2500,1000. 2: 3000
     collection: 3000,2500,1000. 1: 2500
     collection: 3000,2500,1000. 0: 1000
     3000
     2500
     1000
     6500
 */
 ```
 
 #### reduceRightAsync.factory( \[options,] reducer )
 
 Returns a `function` which invokes a function once for each element in a `collection`, iterating from right to left.
 
 ```javascript
 function reducer( acc, value, index, next ) {
     setTimeout( onTimeout, value );
     function onTimeout() {
         console.log( value );
         acc.sum += value;
         next( null, acc );
     }
 }
 
 function done( error, acc ) {
     if ( error ) {
         throw error;
     }
     console.log( acc.sum );
 }
 
 var f = reduceRightAsync.factory( reducer );
 
 var arr1 = [ 1000, 2500, 3000 ];
 
 var acc1 = {
     'sum': 0
 };
 
 f( arr1, acc1, done );
 /* =>
     3000
     2500
     1000
     6500
 */
 
 var arr2 = [ 100, 250, 300 ];
 
 var acc2 = {
     'sum': 0
 };
 
 f( arr2, acc2, done );
 /* =>
     300
     250
     100
     650
 */
 ```
 
 The function accepts the same `options` as `reduceRightAsync()`.
 
 </section>
 
 <!-- /.usage -->
 
 <!-- Package usage notes. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
 
 <section class="notes">
 
 ## Notes
 
 -   A `collection` may be either an [`Array`][mdn-array], [`Typed Array`][mdn-typed-array], or an array-like [`Object`][mdn-object] (excluding `strings` and `functions`).
 -   If a provided function calls the `next` callback with a truthy `error` argument, the function suspends execution and immediately calls the `done` callback for subsequent `error` handling.
 -   The function invokes the `done` callback with the `accumulator` provided as the second argument. If provided an empty `collection`, the function invokes the `done` callback with the `initial` value as the second argument.
 -   The function does **not** support dynamic `collection` resizing.
 -   The function does **not** skip `undefined` elements.
 -   When processing `collection` elements concurrently, **beware** of race conditions when updating an accumulator. This is especially true when an accumulator is a primitive (e.g., a `number`). In general, prefer `object` accumulators, as objects are passed by reference, not by value.
 -   **Neither** `reduceRightAsync` nor the function returned by the `factory` method **guarantee** asynchronous execution. To guarantee asynchrony, 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`).
 
 </section>
 
 <!-- /.notes -->
 
 <!-- Package usage examples. -->
 
 <section class="examples">
 
 ## Examples
 
 <!-- eslint no-undef: "error" -->
 
 ```javascript
 var resolve = require( 'path' ).resolve;
 var readFile = require( '@stdlib/fs/read-file' );
 var reduceRightAsync = require( '@stdlib/utils/async/reduce-right' );
 
 var files = [
     resolve( __dirname, 'package.json' ),
     resolve( __dirname, 'README.md' )
 ];
 
 function done( error, acc ) {
     if ( error ) {
         throw error;
     }
     console.log( acc.count );
 }
 
 function read( acc, file, next ) {
     var opts = {
         'encoding': 'utf8'
     };
     readFile( file, opts, onFile );
 
     function onFile( error ) {
         if ( error ) {
             return next( null, acc );
         }
         acc.count += 1;
         next( null, acc );
     }
 }
 
 var acc = {
     'count': 0
 };
 reduceRightAsync( files, acc, read, done );
 ```
 
 </section>
 
 <!-- /.examples -->
 
 <!-- Section to include cited references. If references are included, add a horizontal rule *before* the section. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
 
 <section class="references">
 
 </section>
 
 <!-- /.references -->
 
 <!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->
 
 <section class="links">
 
 [mdn-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array
 
 [mdn-typed-array]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray
 
 [mdn-object]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object
 
 </section>
 
 <!-- /.links -->