npm package: @stdlib/streams-node-from-constant
Description: Create a readable stream which always streams the same value.
Author: The Stdlib Authors
Latest version: 0.2.3

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  <summary>
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</details>

# Constant Stream

[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url] <!-- [![dependencies][dependencies-image]][dependencies-url] -->

> Create a [readable stream][readable-stream] which always streams the same value.

<section class="installation">

## Installation

```bash
npm install @stdlib/streams-node-from-constant
```

</section>

<section class="usage">

## Usage

```javascript
var constantStream = require( '@stdlib/streams-node-from-constant' );
```

<a name="constant-stream"></a>

#### 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`.

</section>

<!-- /.usage -->

* * *

<section class="notes">

## 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.

</section>

<!-- /.notes -->

* * *

<section class="examples">

## Examples

<!-- eslint no-undef: "error" -->

```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 );
```

</section>

<!-- /.examples -->

<!-- Section for describing a command-line interface. -->



<!-- Section for related `stdlib` packages. Do not manually edit this section, as it is automatically populated. -->

<section class="related">

## See Also

-   <span class="package-name">[`@stdlib/streams-node-from-constant-cli`][@stdlib/streams-node-from-constant-cli]</span><span class="delimiter">: </span><span class="description">CLI package for use as a command-line utility.</span>
-   <span class="package-name">[`@stdlib/streams-node/from-array`][@stdlib/streams/node/from-array]</span><span class="delimiter">: </span><span class="description">create a readable stream from an array-like object.</span>
-   <span class="package-name">[`@stdlib/streams-node/from-iterator`][@stdlib/streams/node/from-iterator]</span><span class="delimiter">: </span><span class="description">create a readable stream from an iterator.</span>

</section>

<!-- /.related -->

<!-- Section for all links. Make sure to keep an empty line after the `section` element and another before the `/section` close. -->


<section class="main-repo" >

* * *

## 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 &copy; 2016-2026. The Stdlib [Authors][stdlib-authors].

</section>

<!-- /.stdlib -->

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[cli-section]: https://github.com/stdlib-js/streams-node-from-constant#cli
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[@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

<!-- <related-links> -->

[@stdlib/streams/node/from-array]: https://www.npmjs.com/package/@stdlib/streams-node-from-array

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