Constant Stream

Create a readable stream which always streams the same value.

Installation

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

Usage

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

constantStream( value[, options] )

Returns a readable stream which always streams the same value.

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 should operate in objectMode. 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. Default: '\n'.
• iter: number of iterations.

To set stream options,

var opts = {
    'objectMode': true,
    'encoding': 'utf8',
    'highWaterMark': 64
};

var stream = constantStream( 'beep', opts );

By default, the function returns a stream which streams an infinite number of values (i.e., the stream will never end). To limit the number of streamed values, set the iter option.

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, a returned stream delineates streamed values using a newline character. To specify an alternative separator, set the sep option.

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 which always stream the same provided value.

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 which always stream the same value.

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.

var createStream = constantStream.factory();

var stream1 = createStream( 'beep' );
var stream2 = createStream( 'boop' );
// ...

The method accepts the same options as constantStream().

constantStream.objectMode( value[, options] )

This method is a convenience function to create streams which always operate in objectMode.

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(); however, the method will always override the objectMode option in options.

Notes

• In binary mode, a provided value must be a string, Buffer, or Uint8Array.
• In objectMode, null is a reserved value. If provided null, the returned 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.
• 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

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 );

See Also

• @stdlib/streams-node-from-constant-cli: CLI package for use as a command-line utility.
• @stdlib/streams-node/from-array: create a readable stream from an array-like object.
• @stdlib/streams-node/from-iterator: create a readable stream from an iterator.

Notice

This package is part of 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, see the main project repository.

Community

License

See LICENSE.

Copyright

Copyright © 2016-2024. The Stdlib Authors.