04 — Filtering

Goal

Add pendingTodos — a function that returns only the todos that are not yet done. This powers the list --pending flag in the CLI.

Add pendingTodos

// todo.js — add below removeTodo
function pendingTodos(todos) {
  return todos.filter((t) => !t.done);
}

The callback keeps every item where done is falsy (false or undefined — beginner-era items without a done field also pass through, so old data stays compatible).

Updated module.exports

module.exports = {
  readTodos, writeTodos, addTodo, completeTodo, removeTodo, pendingTodos, formatList,
};

Checkpoint

const { pendingTodos } = require('./todo');
const result = pendingTodos([
  { text: 'a', done: true },
  { text: 'b', done: false },
]);
console.log(result.length);    // 1
console.log(result[0].text);   // b

Expected output:

1
b

Why keep formatList unchanged?

pendingTodos returns the same shape as readTodos — an array of todo objects. That means you can pass it straight to formatList without any adapter:

// inside cli.js later
console.log(formatList(pendingTodos(readTodos(FILE))));

Keeping functions focused on one thing (filter vs. format vs. persist) is what makes them composable.