Custom Commands

vimee’s pure function architecture makes it easy to extend with custom commands.

Defining a Custom Command

Since all operations are pure functions, you can compose them to create custom behavior:

import { createInitialContext, processKeystroke, TextBuffer } from "@vimee/core";

function clearLine(ctx: VimContext, buffer: TextBuffer) {
  // Move to start of line, then delete to end
  let result = processKeystroke("0", ctx, buffer);
  result = processKeystroke("d", result.newCtx, buffer);
  result = processKeystroke("$", result.newCtx, buffer);
  return result;
}

Composing Operations

Because vimee is built on pure functions, you can freely compose operations:

function duplicateLine(ctx: VimContext, buffer: TextBuffer) {
  let result = processKeystroke("y", ctx, buffer);
  result = processKeystroke("y", result.newCtx, buffer); // yy — yank line
  result = processKeystroke("p", result.newCtx, buffer); // p — paste below
  return result;
}

Using the Testkit to Verify

You can verify your custom commands work correctly using @vimee/testkit:

import { vim } from "@vimee/testkit";
import { expect, test } from "vitest";

test("clear line removes all content on current line", () => {
  const v = vim("hello world\nsecond line", { cursor: [0, 3] });
  v.type("0d$");

  expect(v.line(0)).toBe("");
  expect(v.line(1)).toBe("second line");
});

test("yy + p duplicates the current line", () => {
  const v = vim("hello\nworld");
  v.type("yyp");

  expect(v.lines()).toEqual(["hello", "hello", "world"]);
});