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The browser project stored tasks in localStorage. This version works in a terminal and writes a JSON file. You will practice arguments, parsing, validation, asynchronous file I/O, and exit status. Create a folder named task-cli and save the following file as task.mjs.

task.mjs

import { readFile, writeFile } from "node:fs/promises";
import { join } from "node:path";

const file = join(process.cwd(), "tasks.json");
const [command, ...args] = process.argv.slice(2);

async function load() {
  try {
    const tasks = JSON.parse(await readFile(file, "utf8"));
    if (!Array.isArray(tasks) || !tasks.every((task) =>
      task && Number.isSafeInteger(task.id) && task.id > 0 &&
      typeof task.title === "string" && typeof task.done === "boolean"
    )) throw new Error("tasks.json must contain valid tasks");
    return tasks;
  } catch (error) {
    if (error?.code === "ENOENT") return [];
    throw error;
  }
}

async function save(tasks) {
  await writeFile(file, `${JSON.stringify(tasks, null, 2)}\n`, "utf8");
}

function parseId(raw) {
  const id = Number(raw);
  if (!Number.isSafeInteger(id) || id < 1) throw new Error("ID must be a positive integer");
  return id;
}

async function main() {
  const tasks = await load();
  if (command === "add") {
    const title = args.join(" ").trim();
    if (!title) throw new Error("Usage: node task.mjs add <title>");
    const id = tasks.reduce((max, task) => Math.max(max, task.id), 0) + 1;
    if (!Number.isSafeInteger(id)) throw new Error("No task IDs available");
    tasks.push({ id, title, done: false });
    await save(tasks);
    console.log(`Added task ${id}`);
  } else if (command === "list") {
    if (tasks.length === 0) console.log("No tasks yet");
    for (const task of tasks) {
      console.log(`${task.id}. [${task.done ? "x" : " "}] ${task.title}`);
    }
  } else if (command === "done" || command === "delete") {
    const id = parseId(args[0]);
    const index = tasks.findIndex((task) => task.id === id);
    if (index === -1) throw new Error(`Task ${id} not found`);
    if (command === "done") tasks[index].done = true;
    else tasks.splice(index, 1);
    await save(tasks);
    console.log(command === "done" ? `Completed task ${id}` : `Deleted task ${id}`);
  } else {
    throw new Error("Usage: node task.mjs add <title> | list | done <id> | delete <id>");
  }
}

try {
  await main();
} catch (error) {
  console.error(error instanceof Error ? error.message : String(error));
  process.exitCode = 1;
}

Run these commands in order:

node task.mjs add Read about promises
node task.mjs add Write tests
node task.mjs list
node task.mjs done 1
node task.mjs delete 2
node task.mjs list

You should end with 1. [x] Read about promises. process.argv.slice(2) drops the Node and script paths. load() treats a missing file as an empty task list, but reports malformed JSON or invalid task records instead of erasing them. parseId() rejects missing, fractional, and negative IDs. The next ID is one larger than the greatest remaining ID; deleting the highest-numbered task can cause that ID to be reused on the next add. A production system would use a persistent ID generator.

writeFile() replaces the whole file. That is fine for this single-process learning tool, but simultaneous processes could overwrite one another. A real multi-user service needs a database or a coordinated write strategy. Also, very large task files should not be loaded fully into memory.

Check your work: Run done 999, done nope, and add without a title. Each should print a useful error and exit non-zero. Open tasks.json to confirm it is readable JSON, then rerun list from the same directory.

Extend it: Add list --open and list --done, and extract filtering into a pure function with tests. For a more robust save, write a temporary file and rename it once the write succeeds, while still considering concurrency.

Written By: Shiva Srivastava

Project 2: Node.js Task CLI

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