I am very confused on Deno documentation. It has ReadableStream and WritableStream API, but it doesn’t have a documentation to use it.
I want to read from ReadableStream and write to WritableStream, how can I do that in Deno?
Advertisement
Answer
I want to read from
ReadableStreamand write toWritableStream, how can I do that in Deno?
Here’s a basic TypeScript example demonstrating manual use of the readable and writable parts of a TextEncoderStream (which is a subtype of TransformStream) with verbose console logging:
so-73087438.ts:
JavaScript
x
34
34
1
const decoder = new TextDecoder();2
const decode = (chunk: Uint8Array): string =>3
decoder.decode(chunk, { stream: true });4
5
const stream = new TextEncoderStream();6
7
(async () => {8
for await (const chunk of stream.readable) {9
const message = `Chunk read from stream: "${decode(chunk)}"`;10
console.log(message);11
}12
console.log("Stream closed");13
})();14
15
const texts = ["hello", "world"];16
17
const writer = stream.writable.getWriter();18
const write = async (chunk: string): Promise<void> => {19
await writer.ready;20
await writer.write(chunk);21
};22
23
for (const str of texts) {24
const message = `Writing chunk to stream: "${str}"`;25
console.log(message);26
await write(str);27
}28
29
console.log("Releasing lock on stream writer");30
writer.releaseLock();31
console.log("Closing stream");32
await stream.writable.close();33
34
JavaScript
1
15
15
1
% deno --version2
deno 1.24.0 (release, x86_64-apple-darwin)3
v8 10.4.132.204
typescript 4.7.45
6
% deno run so-73087438.ts7
Writing chunk to stream: "hello"8
Chunk read from stream: "hello"9
Writing chunk to stream: "world"10
Chunk read from stream: "world"11
Releasing lock on stream writer12
Closing stream13
Stream closed14
15
Covering the entirety of the API for WHATWG Streams is out of scope for a Stack Overflow answer. The following links will answer any question you could ask about these streams: