ReadableStream.pipeThrough()
The pipeThrough()
method of the ReadableStream
interface provides a chainable way of piping the current
stream through a transform stream or any other writable/readable pair.
Piping a stream will generally lock it for the duration of the pipe, preventing other readers from locking it.
Syntax
pipeThrough(transformStream)
pipeThrough(transformStream, options)
Parameters
transformStream
-
A
TransformStream
(or an object with the structure{writable, readable}
) consisting of a readable stream and a writable stream working together to transform some data from one form to another. Data written to thewritable
stream can be read in some transformed state by thereadable
stream. For example, aTextDecoder
, has bytes written to it and strings read from it, while a video decoder has encoded bytes written to it and uncompressed video frames read from it. options
Optional-
The options that should be used when piping to the
writable
stream. Available options are:-
preventClose
: If this is set totrue
, the sourceReadableStream
closing will no longer cause the destinationWritableStream
to be closed. The method will return a fulfilled promise once this process completes, unless an error is encountered while closing the destination in which case it will be rejected with that error. -
preventAbort
: If this is set totrue
, errors in the sourceReadableStream
will no longer abort the destinationWritableStream
. The method will return a promise rejected with the source's error, or with any error that occurs during aborting the destination. -
preventCancel
: If this is set totrue
, errors in the destinationWritableStream
will no longer cancel the sourceReadableStream
. In this case the method will return a promise rejected with the source's error, or with any error that occurs during canceling the source. In addition, if the destination writable stream starts out closed or closing, the source readable stream will no longer be canceled. In this case the method will return a promise rejected with an error indicating piping to a closed stream failed, or with any error that occurs during canceling the source. -
signal
: If set to anAbortSignal
object, ongoing pipe operations can then be aborted via the correspondingAbortController
.
-
Return value
The readable
side of the transformStream
.
Exceptions
TypeError
-
The
writable
and/orreadable
property oftransformStream
are undefined.
Examples
In the following example (see Unpack chunks
of a PNG for the full code running live, and png-transform-stream
for the source code), an image is fetched and its body retrieved as a
ReadableStream
. Next, we log the contents of the readable stream, use
pipeThrough()
to send it to a new function that creates a gray-scaled
version of the stream, then log the new stream's contents too.
// Fetch the original image
fetch('png-logo.png')
// Retrieve its body as ReadableStream
.then(response => response.body)
.then(rs => logReadableStream('Fetch Response Stream', rs))
// Create a gray-scaled PNG stream out of the original
.then(body => body.pipeThrough(new PNGTransformStream()))
.then(rs => logReadableStream('PNG Chunk Stream', rs))
Specifications
Specification |
---|
Streams Standard # ref-for-rs-pipe-through② |
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