@nick/is/reader

isReader

Signature

function isReader(it: unknown): it is Reader;

Checks if a given value is an asynchronous reader, which is an object that implements the read method as per Deno's Reader interface.

Parameters

Name	Info
it	The value to check.

Returns

true if the value is an asynchronous Reader, false otherwise.

Category

I/O

Examples

import { isReader } from "jsr:@nick/is/reader";

const file = await Deno.open("file.txt");
isReader(file); // true

const socket = new WebSocket("ws://example.com");
isReader(socket); // false

Reader

An abstract interface which when implemented provides an interface to read bytes into an array buffer asynchronously.

Category

I/O

Methods

read

read(
    p: Uint8Array,
  ): Promise<number | null>;

Reads up to p.byteLength bytes into p. It resolves to the number of bytes read (0 < n <= p.byteLength) and rejects if any error encountered. Even if read() resolves to n < p.byteLength, it may use all of p as scratch space during the call. If some data is available but not p.byteLength bytes, read() conventionally resolves to what is available instead of waiting for more.

When read() encounters end-of-file condition, it resolves to EOF (null). When read() encounters an error, it rejects with an error.

Callers should always process the n > 0 bytes returned before considering the EOF (null). Doing so correctly handles I/O errors that happen after reading some bytes and also both of the allowed EOF behaviors.

Implementations should not retain a reference to p.

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