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Deno Quick Reference ↩

Deno project This document gathers Deno hints and tips.

Covered topics include: Deno versus Node.js, Deno commands, Deno runtime, Windows specific fixes.

Deno versus Node.js

  1. CommonJS versus ECMAScript modules

    Deno supports only the ECMAScript modules (short ES modules or ESM) while Node.js supports both formats for the CommonJS and ECMAScript modules.

    const http = require('http'); /* CommonJS */
import { serve } from "https://deno.land/std/http/server.ts"; /* ECMAScript */

    🔎 Deno supports the @deno-types compiler hint to specify a type definition file when type checking instead of the imported JavaScript file (see "Providing types when importing").

  2. Runtime versus Standard library

    Unlike Node.js Deno has a lightweight built-in runtime of around 130 methods, functions and classes. See section Deno Runtime for more details.

Deno Commands ▲

deno cache

  • deno cache makes sure we have a local copy of our code's dependencies without having to run it
    Note: It makes think of command npm install on Node.js.
  • With the --reload flag deno cache forces the dependencies to be downloaded. A comma-separated list of modules that must be reloaded can be sent as a parameter to the --reload flag.

deno doc

The following command displays the documentation for method serve of the standard library's HTTP module.

> deno doc https://deno.land/std@0.208.0/http/server.ts serve
Defined in https://deno.land/std@0.208.0/http/server.ts:572:0

function serve(addr: string | HTTPOptions): Server
  Serves HTTP requests with the given handler.

  You can specify an object with a port and hostname option, which is the address to listen on.
  The default is port 8000 on hostname "0.0.0.0".

  The below example serves with the port 8000.
  [...]

The following command displays the documentation for method writeFile of the Deno built-in API:

> deno doc --builtin Deno.writeFile
Defined in lib.deno.d.ts:2048:2

function writeFile(path: string | URL, data: Uint8Array, options?: WriteFileOptions): Promise
  Write `data` to the given `path`, by default creating a new file if needed,
  else overwriting.

  ```ts
  const encoder = new TextEncoder();
  const data = encoder.encode("Hello world\n");
  await Deno.writeFile("hello1.txt", data);  // overwrite "hello1.txt" or create it
  await Deno.writeFile("hello2.txt", data, {create: false});  // only works if "hello2.txt" exists
  await Deno.writeFile("hello3.txt", data, {mode: 0o777});  // set permissions on new file
  await Deno.writeFile("hello4.txt", data, {append: true});  // add data to the end of the file
  ```

  Requires `allow-write` permission, and `allow-read` if `options.create` is `false`.

Deno Runtime ▴

Two types of functions are available on Deno without any imports: Web APIs and the Deno built-in API. Code written using Web APIs can be bundled and run in the browser with no transformations.

  1. WebAssembly namespace

    Interfaces in the WebAssembly namespace are:

    > set NO_COLOR=true & deno doc --builtin WebAssembly |findstr /r /c:"^[ ][ ]interface"
interface GlobalDescriptor
interface MemoryDescriptor
interface ModuleExportDescriptor
interface ModuleImportDescriptor
interface TableDescriptor
interface WebAssemblyInstantiatedSource

    Functions in the WebAsssembly namepspace are:

    > set NO_COLOR=true & deno doc --builtin WebAssembly |findstr /r /c:"^[ ][ ]function"
function compile(bytes: BufferSource): Promise
function compileStreaming(source: Response | Promise): Promise
function instantiate(bytes: BufferSource, importObject?: Imports): Promise
function instantiate(moduleObject: Module, importObject?: Imports): Promise
function instantiateStreaming(response: Response | PromiseLike, importObject?: Imports): Promise
function validate(bytes: BufferSource): boolean

    🔎 The above functions are defined in the MDN Web Docs.

  2. Deno namespace

    Interfaces in the Deno namespace are:

    > set NO_COLOR=true & deno doc --builtin Deno |findstr /r /c:"^[ ][ ]interface"
interface MemoryUsage
interface TestDefinition
interface Reader
interface ReaderSync
interface Writer
interface WriterSync
interface Closer
interface Seeker
interface SeekerSync
interface OpenOptions
interface ReadFileOptions
interface MkdirOptions
interface MakeTempOptions
interface RemoveOptions
interface FileInfo
interface DirEntry
interface WriteFileOptions
interface Metrics
interface FsEvent
interface FsWatcher extends AsyncIterable
interface RunOptions
[...]

    read functions in the Deno namespace are:

    > set NO_COLOR=true & deno doc --builtin Deno |findstr /r /c:"^[ ][ ]function read"
function readSync(rid: number, buffer: Uint8Array): number | null
function read(rid: number, buffer: Uint8Array): Promise<number | null>
function readAll(r: Reader): Promise<Uint8Array>
function readAllSync(r: ReaderSync): Uint8Array
function readTextFileSync(path: string | URL): string
function readTextFile(path: string | URL, options?: ReadFileOptions): Promise
function readFileSync(path: string | URL): Uint8Array
function readFile(path: string | URL, options?: ReadFileOptions): Promise
function readDirSync(path: string | URL): Iterable
function readDir(path: string | URL): AsyncIterable
function readLinkSync(path: string | URL): string
function readLink(path: string | URL): Promise

    🔎 We can evaluate the code example presented in the readTextFile documentation:

    > deno doc --builtin Deno.readTextFile
Defined in lib.deno.d.ts:1725:2
 
function readFile(path: string | URL, options?: ReadFileOptions):  Promise
  Reads and resolves to the entire contents of a file as an array of bytes.
  `TextDecoder` can be used to transform the bytes to string if required.
  Reading a directory returns an empty data array.
 
  ```ts
  const data = await Deno.readTextFile("hello.txt");
  console.log(data);
   ```
 
  Requires `allow-read` permission.

    For instance:

    > deno eval "const data = await Deno.readTextFile('.gitignore'); console.log(data);"
.idea/
.project
.settings/
.vscode/
*_LOCAL/
out/
target/

Windows specific fixes

1.14.2 (2021.09.28)

  • fix: subprocess kill support on windows (#12134).

mics/June 2024 ▲