https://github.com/stdlib-js/streams-node-from-constant
Create a readable stream which always streams the same value.
https://github.com/stdlib-js/streams-node-from-constant
const constant javascript node node-js nodejs readable repeat stdlib stream streams util utilities utility utils
Last synced: about 2 months ago
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Create a readable stream which always streams the same value.
- Host: GitHub
- URL: https://github.com/stdlib-js/streams-node-from-constant
- Owner: stdlib-js
- License: apache-2.0
- Created: 2021-06-15T17:46:55.000Z (almost 5 years ago)
- Default Branch: main
- Last Pushed: 2024-12-01T08:58:05.000Z (over 1 year ago)
- Last Synced: 2025-02-01T07:32:28.609Z (about 1 year ago)
- Topics: const, constant, javascript, node, node-js, nodejs, readable, repeat, stdlib, stream, streams, util, utilities, utility, utils
- Language: JavaScript
- Homepage: https://github.com/stdlib-js/stdlib
- Size: 1.77 MB
- Stars: 1
- Watchers: 3
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGELOG.md
- Contributing: CONTRIBUTING.md
- License: LICENSE
- Code of conduct: CODE_OF_CONDUCT.md
- Citation: CITATION.cff
- Security: SECURITY.md
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README
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# Constant Stream
[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url]
> Create a [readable stream][readable-stream] which always streams the same value.
## Installation
```bash
npm install @stdlib/streams-node-from-constant
```
Alternatively,
- To load the package in a website via a `script` tag without installation and bundlers, use the [ES Module][es-module] available on the [`esm`][esm-url] branch (see [README][esm-readme]).
- If you are using Deno, visit the [`deno`][deno-url] branch (see [README][deno-readme] for usage intructions).
- For use in Observable, or in browser/node environments, use the [Universal Module Definition (UMD)][umd] build available on the [`umd`][umd-url] branch (see [README][umd-readme]).
- To use as a general utility for the command line, install the corresponding [CLI package][cli-section] globally.
The [branches.md][branches-url] file summarizes the available branches and displays a diagram illustrating their relationships.
To view installation and usage instructions specific to each branch build, be sure to explicitly navigate to the respective README files on each branch, as linked to above.
## Usage
```javascript
var constantStream = require( '@stdlib/streams-node-from-constant' );
```
#### constantStream( value\[, options] )
Returns a [readable stream][readable-stream] which **always** streams the **same** `value`.
```javascript
var inspectStream = require( '@stdlib/streams-node-inspect-sink' );
var iStream;
var stream;
function log( chunk, i ) {
console.log( chunk.toString() );
if ( i === 10 ) {
stream.destroy();
}
}
stream = constantStream( 'beep' );
iStream = inspectStream( log );
stream.pipe( iStream );
```
The function accepts the following `options`:
- **objectMode**: specifies whether a [stream][stream] should operate in [objectMode][object-mode]. Default: `false`.
- **encoding**: specifies how `Buffer` objects should be decoded to `strings`. Default: `null`.
- **highWaterMark**: specifies the maximum number of bytes to store in an internal buffer before pausing streaming.
- **sep**: separator used to join streamed data. This option is only applicable when a stream is **not** in [objectMode][object-mode]. Default: `'\n'`.
- **iter**: number of iterations.
To set [stream][stream] `options`,
```javascript
var opts = {
'objectMode': true,
'encoding': 'utf8',
'highWaterMark': 64
};
var stream = constantStream( 'beep', opts );
```
By default, the function returns a [stream][stream] which streams an infinite number of values (i.e., the [stream][stream] will **never** end). To limit the number of streamed values, set the `iter` option.
```javascript
var inspectStream = require( '@stdlib/streams-node-inspect-sink' );
function log( chunk ) {
console.log( chunk.toString() );
}
var opts = {
'iter': 10
};
var stream = constantStream( 'beep', opts );
var iStream = inspectStream( log );
stream.pipe( iStream );
```
By default, when not operating in [objectMode][object-mode], a returned [stream][stream] delineates streamed values using a newline character. To specify an alternative separator, set the `sep` option.
```javascript
var inspectStream = require( '@stdlib/streams-node-inspect-sink' );
function log( chunk ) {
console.log( chunk.toString() );
}
var opts = {
'iter': 10,
'sep': ','
};
var stream = constantStream( 'beep', opts );
var iStream = inspectStream( log );
stream.pipe( iStream );
```
* * *
#### constantStream.factory( \[value, ]\[options] )
Returns a `function` for creating [readable streams][readable-stream] which **always** stream the **same** provided `value`.
```javascript
var opts = {
'objectMode': true,
'encoding': 'utf8',
'highWaterMark': 64
};
var createStream = constantStream.factory( opts );
```
If provided a `value` to stream, the returned function returns [readable streams][readable-stream] which **always** stream the **same** `value`.
```javascript
var createStream = constantStream.factory( 'beep' );
var stream1 = createStream();
var stream2 = createStream();
// ...
```
If not provided a `value` to stream, the returned function requires that a `value` be provided at each invocation.
```javascript
var createStream = constantStream.factory();
var stream1 = createStream( 'beep' );
var stream2 = createStream( 'boop' );
// ...
```
The method accepts the same `options` as [`constantStream()`](#constant-stream).
* * *
#### constantStream.objectMode( value\[, options] )
This method is a convenience function to create [streams][stream] which **always** operate in [objectMode][object-mode].
```javascript
var inspectStream = require( '@stdlib/streams-node-inspect-sink' );
function log( v ) {
console.log( v );
}
var value = {
'beep': 'boop'
};
var opts = {
'iter': 10
};
var stream = constantStream.objectMode( value, opts );
opts = {
'objectMode': true
};
var iStream = inspectStream( opts, log );
stream.pipe( iStream );
```
This method accepts the same `options` as [`constantStream()`](#constant-stream); however, the method will **always** override the [`objectMode`][object-mode] option in `options`.
* * *
## Notes
- In binary mode, a provided `value` must be a `string`, `Buffer`, or `Uint8Array`.
- In [`objectMode`][object-mode], `null` is a reserved value. If provided `null`, the returned [stream][stream] will prematurely end.
- If provided an `object` reference, the `value` is **not** copied. To avoid unwanted mutation, copy the `value` **before** creating a [stream][stream].
- In older Node.js environments, `Uint8Array` contents may be copied to a new `Buffer` object due to changes in the underlying Node.js APIs.
- If the `factory` method is provided only one argument and that argument is an `object` (either empty or not containing any recognized `options` properties), the method treats the argument as a value to be streamed, **not** as an `options` argument.
* * *
## Examples
```javascript
var inspectStream = require( '@stdlib/streams-node-inspect-sink' );
var constantStream = require( '@stdlib/streams-node-from-constant' );
function log( v ) {
console.log( v.toString() );
}
var opts = {
'objectMode': true,
'iter': 10
};
var stream = constantStream( 3.14, opts );
opts = {
'objectMode': true
};
var iStream = inspectStream( opts, log );
stream.pipe( iStream );
```
* * *
## CLI
## Installation
To use as a general utility, install the CLI package globally
```bash
npm install -g @stdlib/streams-node-from-constant-cli
```
### Usage
```text
Usage: constant-stream [options]
Options:
-h, --help Print this message.
-V, --version Print the package version.
--sep sep Separator used to join streamed data. Default: '\n'.
-n, --iter iterations Number of iterations.
```
### Notes
- In accordance with POSIX convention, a trailing newline is **always** appended to generated output prior to exit.
### Examples
```bash
$ constant-stream 'beep' -n 10
```
* * *
## See Also
- [`@stdlib/streams-node/from-array`][@stdlib/streams/node/from-array]: create a readable stream from an array-like object.
- [`@stdlib/streams-node/from-iterator`][@stdlib/streams/node/from-iterator]: create a readable stream from an iterator.
* * *
## Notice
This package is part of [stdlib][stdlib], a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.
For more information on the project, filing bug reports and feature requests, and guidance on how to develop [stdlib][stdlib], see the main project [repository][stdlib].
#### Community
[![Chat][chat-image]][chat-url]
---
## License
See [LICENSE][stdlib-license].
## Copyright
Copyright © 2016-2026. The Stdlib [Authors][stdlib-authors].
[npm-image]: http://img.shields.io/npm/v/@stdlib/streams-node-from-constant.svg
[npm-url]: https://npmjs.org/package/@stdlib/streams-node-from-constant
[test-image]: https://github.com/stdlib-js/streams-node-from-constant/actions/workflows/test.yml/badge.svg?branch=main
[test-url]: https://github.com/stdlib-js/streams-node-from-constant/actions/workflows/test.yml?query=branch:main
[coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/streams-node-from-constant/main.svg
[coverage-url]: https://codecov.io/github/stdlib-js/streams-node-from-constant?branch=main
[chat-image]: https://img.shields.io/badge/zulip-join_chat-brightgreen.svg
[chat-url]: https://stdlib.zulipchat.com
[stdlib]: https://github.com/stdlib-js/stdlib
[stdlib-authors]: https://github.com/stdlib-js/stdlib/graphs/contributors
[cli-section]: https://github.com/stdlib-js/streams-node-from-constant#cli
[cli-url]: https://github.com/stdlib-js/streams-node-from-constant/tree/cli
[@stdlib/streams-node-from-constant]: https://github.com/stdlib-js/streams-node-from-constant/tree/main
[umd]: https://github.com/umdjs/umd
[es-module]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules
[deno-url]: https://github.com/stdlib-js/streams-node-from-constant/tree/deno
[deno-readme]: https://github.com/stdlib-js/streams-node-from-constant/blob/deno/README.md
[umd-url]: https://github.com/stdlib-js/streams-node-from-constant/tree/umd
[umd-readme]: https://github.com/stdlib-js/streams-node-from-constant/blob/umd/README.md
[esm-url]: https://github.com/stdlib-js/streams-node-from-constant/tree/esm
[esm-readme]: https://github.com/stdlib-js/streams-node-from-constant/blob/esm/README.md
[branches-url]: https://github.com/stdlib-js/streams-node-from-constant/blob/main/branches.md
[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/streams-node-from-constant/main/LICENSE
[stream]: https://nodejs.org/api/stream.html
[object-mode]: https://nodejs.org/api/stream.html#stream_object_mode
[readable-stream]: https://nodejs.org/api/stream.html
[@stdlib/streams/node/from-array]: https://github.com/stdlib-js/streams-node-from-array
[@stdlib/streams/node/from-iterator]: https://github.com/stdlib-js/streams-node-from-iterator