ReadFile from URL in Deno

Question

I'm trying this code but it gives me an error:

const decoder = new TextDecoder("utf-8");
const url = new URL("https://github.com/denoland/deno/releases/download/v1.30.3/lib.deno.d.ts")

const text = await Deno.readFile(url);
console.log(decoder.decode(text));

I want to know how to make this work

Answer 1

The methods Deno.read* are for interacting with the local file system.

To download the contents of a remote resource, you can use the web standard fetch API — just like in a browser — and getting a textual representation of the resource content is also the same. Here's a basic example which will download the type declaration file in your question and print it to stdout:

main.ts:

async function fetchText(url: URL | string): Promise<string> {
  const response = await fetch(url);
  if (!response.ok) throw new Error(`Response not OK (${response.status})`);
  return response.text();
}

const url =
  "https://github.com/denoland/deno/releases/download/v1.30.3/lib.deno.d.ts";

const text = await fetchText(url);
console.log(text);

I can run it in the terminal and redirect the output to a file called types_download like this:

% deno --version
deno 1.30.3 (release, aarch64-apple-darwin)
v8 10.9.194.5
typescript 4.9.4

% deno run --allow-net main.ts > types_download

And then view the first 10 lines of the file:

% head --lines=10 types_download
// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.

/// <reference no-default-lib="true" />
/// <reference lib="esnext" />
/// <reference lib="deno.net" />

/** Deno provides extra properties on `import.meta`. These are included here
 * to ensure that these are still available when using the Deno namespace in
 * conjunction with other type libs, like `dom`.
 *

---

By the way: this type declaration file is available directly from the Deno CLI using the deno types command:

% deno types > types_cli      

% head --lines=10 types_cli 
// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.

/// <reference no-default-lib="true" />
/// <reference lib="esnext" />
/// <reference lib="deno.net" />

/** Deno provides extra properties on `import.meta`. These are included here
 * to ensure that these are still available when using the Deno namespace in
 * conjunction with other type libs, like `dom`.
 *