03 — The remove command

Goal

Add removeTodo — a function that drops one todo by index and returns the rest as a new array.

Add removeTodo

// todo.js — add below completeTodo
function removeTodo(todos, index) {
  return todos.filter((_, i) => i !== index);
}

Array.filter visits every element. _ is the element itself (unused); i is its index. The callback keeps every item whose index is not the target — equivalent to slicing the array around that position, but shorter.

Updated module.exports

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

Checkpoint

const { removeTodo } = require('./todo');
const result = removeTodo([{ text: 'a' }, { text: 'b' }], 0);
console.log(JSON.stringify(result)); // [{"text":"b"}]

Expected output: [{"text":"b"}]

Why not splice?

Array.splice mutates the original array, which makes functions harder to compose and test. filter returns a new array, keeping the same pattern as completeTodo — both functions are pure: same input always produces same output, no side effects.