`keydown`

Keyboard event stream that emits only keydown events. Shares underlying listeners per EventTarget.

npm install --save cereb

Basic Usage

import { keydown } from "cereb";

keydown(window).on((signal) => {
  console.log("Key pressed:", signal.value.code);
});

Signature

function keydown(target: EventTarget, options?: KeydownOptions): Stream<KeyboardSignal>

Options

Option	Type	Default	Description
`code`	`KeyCode \| KeyCode[]`	-	Filter by physical key code(s)
`modifiers`	`ModifierKey[]`	-	Filter by modifier keys (OR logic)
`preventDefault`	`boolean`	`true`	Call preventDefault on matching events
`allowRepeat`	`boolean`	`false`	Allow repeated keydown events

Signal Value

Property	Type	Description
`phase`	`"down"`	Always “down” for keydown
`key`	`string`	Logical key value (e.g., ”+”, “a”, “Meta”)
`code`	`string`	Physical key code (e.g., “Equal”, “KeyA”)
`repeat`	`boolean`	True if repeated from holding key
`altKey`	`boolean`	Alt key pressed
`ctrlKey`	`boolean`	Ctrl key pressed
`metaKey`	`boolean`	Meta (Cmd/Win) key pressed
`shiftKey`	`boolean`	Shift key pressed
`originalEvent`	`KeyboardEvent`	Original DOM event

Examples

Zoom with +/- Keys

keydown(window, { code: ["Equal", "Minus"] }).on((signal) => {
  const zoomIn = signal.value.code === "Equal";
  setScale(scale * (zoomIn ? 1.2 : 0.8));
});

Undo/Redo Shortcut

// Cmd+Z / Ctrl+Z for undo
keydown(window, {
  code: "KeyZ",
  modifiers: ["meta", "ctrl"]
}).on(handleUndo);

// Cmd+Shift+Z / Ctrl+Shift+Z for redo
keydown(window, {
  code: "KeyZ",
  modifiers: ["meta", "ctrl"]
}).on((signal) => {
  if (signal.value.shiftKey) {
    handleRedo();
  }
});

Allow Key Repeat

// Continuous scrolling while holding arrow key
keydown(window, {
  code: ["ArrowUp", "ArrowDown"],
  allowRepeat: true
}).on((signal) => {
  const direction = signal.value.code === "ArrowUp" ? -1 : 1;
  scroll(direction * 10);
});