Business logic
- Node.js course
- Beginner
- Lesson 114/116
- 6 min
Write business rules with functions and conditional logic.
Business logic functions
We set up the data model; now we add business logic. We will write two functions: addTask(title) adds a new task, completeTask(id) marks a task as done.
addTask auto-generates an id: const id = tasks.length + 1;. Each new task gets the next number. It builds the object with createTask and appends it with tasks.push. completeTask finds the task with tasks.find and sets task.done = true. These two functions form the core behavior of the app. We take the previous lesson's solution and add them.
Searching with find
The completeTask function uses tasks.find. find returns the first item that matches a condition. Example: tasks.find(function(t) { return t.id === id; }). This finds the task whose id matches.
We update the found task with if (task) { task.done = true; }. The if (task) check guards against the case where find returns undefined when no id matches. This is a real use of conditional logic: update only if the task exists. We will reuse the same pattern later with filter to count completed tasks.
Practice Add the addTask and completeTask functions
Take the previous lesson's solution. Add addTask(title): generate id with const id = tasks.length + 1;, append with tasks.push(createTask(id, title)). Add completeTask(id): find with tasks.find, set task.done = true. The last lines are ready: addTask("Email"); completeTask(1); console.log(tasks[0].done);
Starter code
const path = require("path");
const DATA_FILE = path.join("data", "tasks.json");
function createTask(id, title) {
return { id: id, title: title, done: false };
}
let tasks = [];
tasks.push(createTask(1, "Shopping"));
console.log(tasks.length);
// Add the addTask and completeTask functions
// write here
addTask("Email");
completeTask(1);
console.log(tasks[0].done);Sample solution
const path = require("path");
const DATA_FILE = path.join("data", "tasks.json");
function createTask(id, title) {
return { id: id, title: title, done: false };
}
let tasks = [];
tasks.push(createTask(1, "Shopping"));
function addTask(title) {
const id = tasks.length + 1;
tasks.push(createTask(id, title));
}
function completeTask(id) {
const task = tasks.find(function(t) { return t.id === id; });
if (task) { task.done = true; }
}
addTask("Email");
completeTask(1);
console.log(tasks[0].done);Expected output
true
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match each piece to its role
| Term | Meaning |
|---|---|
addTask |
Adds a new task |
completeTask |
Marks a task done |
tasks.find |
Finds by id |
tasks.length + 1 |
Generates a new id |
2 Complete the completeTask body
function completeTask(id) {
const task = tasks.find(function(t) { return t.id === id; });
if (task) { task.____ = true; }
}function completeTask(id) {
const task = tasks.find(function(t) { return t.id === id; });
if (task) { task.done = true; }
}Explanation: The done property is set to true.
3 What does tasks.find return?
tasks.find(function(t) { return t.id === 5; })- All tasks
- The number of tasks
- The first task matching the condition Correct answer
- Yeni bir dizi
Explanation: find returns the first matching item.