Adding toDo app functionability

Closes #2 (closed)

public/js/app.js

-// Obtener referencia a los elementos del DOM
+// Get reference to DOM elements
 const taskList = document.querySelector('.task-list ul');
 const newTaskForm = document.querySelector('form');
 
@@ -16,6 +16,24 @@ document.getElementById('logout-btn').addEventListener('click', async () => {
   }
 });
 
+
+// Function to check if the currently processed task belongs to user account
+async function isValidTask(taskId) {
+  try {
+    const res = await fetch("/api/todos"); 
+    const todos = await res.json();
+    let valid = false;
+
+    todos.forEach(todo => {
+      if (todo._id == taskId)
+        valid = true;
+    });
+    return valid;
+  } catch (err) {
+    console.error("Error loading tasks:", err);
+  }
+}
+
 // Load every task when the page is initialzed
 document.addEventListener('DOMContentLoaded', async () => {
   try {
@@ -78,7 +96,7 @@ newTaskForm.addEventListener('submit', async (e) => {
 
     const newTodo = await res.json();
     taskList.appendChild(createTaskElement(newTodo));
-    input.value = ''; // Limpiar el campo de entrada
+    input.value = ''; // Clear input field
   } catch (err) {
     console.error('Error adding task:', err);
   }
@@ -86,6 +104,12 @@ newTaskForm.addEventListener('submit', async (e) => {
 
 // Mark task as completed
 async function markAsDone(taskId, isDone) {
+  // Input sanitation 
+  if (isNaN(parseInt(taskId, 10)) && typeof(isDone) === 'boolean' && isValidTask(taskId)) {
+    console.error('Invalid task ID, task status is invalid or task does not belong to account');
+    return;
+  }
+
   try {
     const res = await fetch(`/api/todos/${taskId}/done`, {
       method: 'PUT',
@@ -104,6 +128,12 @@ async function markAsDone(taskId, isDone) {
 
 // Erase task
 async function deleteTask(taskId) {
+  // Input sanitation 
+  if (isNaN(parseInt(taskId, 10))) {
+    console.error('Invalid task ID');
+    return;
+  }
+
   try {
     const res = await fetch(`/api/todos/${taskId}`, {
       method: 'DELETE'
@@ -122,6 +152,12 @@ async function deleteTask(taskId) {
 
 // Edit task
 async function updateTask(taskId, newDescription) {
+  // Input sanitation 
+  if (isNaN(parseInt(taskId, 10)) && typeof(newDescription) === 'string' && isValidTask(taskId)) {
+    console.error('Invalid task ID, task status is invalid or task does not belong to account');
+    return;
+  }
+
   try {
     const res = await fetch(`/api/todos/${taskId}/description`, {
       method: 'PUT',