Keypress

Keypress module with promise, async iterator and event target API.

Usage

There are two ways to use this module. You can use the keypress() method, which returns a global instance of the KeyPress class, or you can create a new instance of the KeyPress class. There is no difference between these two ways, except that the keypress() method always returns the same instance, unless the .dispose() method is called. In this case a new instance is returned.

Promise

The keypress module can be used as promise. It reads one chunk from stdin and returns a KeyPressEvent for the first parsed character.

import {
  keypress,
  KeyPressEvent,
} from "https://deno.land/x/cliffy@v0.25.0/keypress/mod.ts";

const event: KeyPressEvent = await keypress();

console.log(
  "type: %s, key: %s, ctrl: %s, meta: %s, shift: %s, alt: %s, repeat: %s",
  event.type,
  event.key,
  event.ctrlKey,
  event.metaKey,
  event.shiftKey,
  event.altKey,
  event.repeat,
);Copy

$ deno run --unstable --reload https://deno.land/x/cliffy@v0.25.0/examples/keypress/promise.tsCopy

Async Iterator

The keypress module can be used as async iterator to iterate over all keypress events. The async iterator reads chunk by chunk from stdin. On each step, it reads one chunk from stdin and emits for each character a keypress event. It pauses reading from stdin before emitting the events, so stdin is not blocked inside the for loop.

import { Keypress, keypress } from "https://deno.land/x/cliffy@v0.25.0/keypress/mod.ts";

for await (const event: KeyPressEvent of keypress()) {
  console.log(
    "type: %s, key: %s, ctrl: %s, meta: %s, shift: %s, alt: %s, repeat: %s",
    event.type,
    event.key,
    event.ctrlKey,
    event.metaKey,
    event.shiftKey,
    event.altKey,
    event.repeat,
  );

  if (event.ctrlKey && event.key === "c") {
    console.log("exit");
    break;
  }
}Copy

$ deno run --unstable --reload https://deno.land/x/cliffy@v0.25.0/examples/keypress/async_iterator.tsCopy

Event Target

The Keypress class extends from the EventTarget class that provides a .addEventListener() method that can be used to register event listeners. The addEventListener method starts an event loop in the background that reads from stdin and emits an event for each input.

i

❗ As long as the event loop is running, stdin is blocked for other resources.

You can stop the event loop with keypress().dispose().

i

❕ The promise and async iterator based solution does not start an event loop in the background.

import {
  keypress,
  KeyPressEvent,
} from "https://deno.land/x/cliffy@v0.25.0/keypress/mod.ts";

keypress().addEventListener("keydown", (event: KeyPressEvent) => {
  console.log(
    "type: %s, key: %s, ctrl: %s, meta: %s, shift: %s, alt: %s, repeat: %s",
    event.type,
    event.key,
    event.ctrlKey,
    event.metaKey,
    event.shiftKey,
    event.altKey,
    event.repeat,
  );

  if (event.ctrlKey && event.key === "c") {
    console.log("exit");
    keypress().dispose();
  }
});Copy

$ deno run --unstable --reload https://deno.land/x/cliffy@v0.25.0/examples/keypress/event_target.tsCopy

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