Creating a Todo Application using Next.js

Next.js is a framework for building server-rendered React applications. It provides a powerful set of features for web development such as automatic code splitting, server-side rendering, and static site generation. In this blog post, we will be creating a simple Todo application using Next.js.

Setting up the project

To get started, you will need to have Node.js and npm (or yarn) installed on your machine. Once you have these dependencies set up, you can create a new Next.js project using the following command:

npx create-next-app my-todo-app

This will create a new directory called “my-todo-app” with the basic file structure and dependencies for a Next.js app.

Creating the Todo List component

In this step, we will create a TodoList component that will display a list of todo items. Create a new file called TodoList.js in the components folder and add the following code:

import React from 'react';

const TodoList = ({ todos }) => {
  return (
    <ul>
      {todos.map((todo) => (
        <li key={todo.id}>
          <span>{todo.text}</span>
          <button>Delete</button>
        </li>
      ))}
    </ul>
  );
};

export default TodoList;

In this code, we are rendering an unordered list and mapping over the todos prop to create a list item for each todo item. We also added a button to delete the todo item.

Adding the Todo Form

Now that we have the TodoList component, we need to create a form to add new todo items. Create a new file called TodoForm.js in the components folder and add the following code:

Copy code
import React, { useState } from 'react';

const TodoForm = ({ addTodo }) => {
  const [text, setText] = useState('');

  const handleSubmit = (e) => {
    e.preventDefault();
    if (!text) return;
    addTodo(text);
    setText('');
  };

  return (
    <form onSubmit={handleSubmit}>
      <input
        type="text"
        value={text}
        onChange={(e) => setText(e.target.value)}
        placeholder="Add Todo..."
      />
    </form>
  );
};

export default TodoForm;


In this code, we are creating a form with an input that allows the user to enter a new todo item. When the form is submitted, it calls the addTodo function with the text of the input as an argument. We are also reset the text state after adding the todo item.

Creating the TodoPage

Create a new file called TodoPage.js in the pages folder and add the following code:

Copy code
import React, { useState } from 'react';
import TodoList from '../components/TodoList';
import TodoForm from '../components/TodoForm';

const TodoPage = () => {
const [todos, setTodos] = useState([]);

const addTodo = (text) => {
setTodos([...todos, { id: todos.length + 1, text }]);
};

const deleteTodo = (id) => {
setTodos(todos.filter((todo) => todo.id !== id));
};

return (
<div>
<TodoForm addTodo={addTodo} />
<TodoList todos={todos} deleteTodo={deleteTodo} />
</div>
);
};

export default TodoPage;


In this file, we are creating a TodoPage component that contains the TodoForm and TodoList components. We are also using React’s useState hook to manage the state of the todo items. The addTodo function is passed down to the TodoForm component as a prop and is called when a new todo item is added. The deleteTodo function is passed down to the TodoList component as a prop and is called when a todo item is deleted.

Adding Routing

Add the following code in your pages/index.js file to redirect users to the TodoPage by default

import TodoPage from './TodoPage';

export default function Home() {
  return <TodoPage />;
}

Now the user will be able to access the TodoPage by visiting the root of your application.

That’s it! You now have a working Todo application built with Next.js. You can customize the application further by adding styles, saving the todo items to a database, or adding more features.

Adding Styles

You can add styles to your Todo application using a CSS preprocessor like SASS or using CSS-in-JS libraries like styled-components.

If you decide to use a CSS preprocessor, you will need to install the necessary dependencies and configure Next.js to use it. You can add the CSS files to the styles directory in the root of your project.

If you prefer to use styled-components, you can install it using npm or yarn by running the following command:

npm install styled-components

And then you can import it in your TodoForm.js and TodoList.js and add styles to your components.

import styled from 'styled-components';

const TodoForm = ({ addTodo }) => {
  // ...
  return (
    <Form onSubmit={handleSubmit}>
      <Input
        type="text"
        value={text}
        onChange={(e) => setText(e.target.value)}
        placeholder="Add Todo..."
      />
    </Form>
  );
};

const Form = styled.form`
  display: flex;
  margin-bottom: 16px;
`;

const Input = styled.input`
  flex: 1;
  padding: 8px;
  border-radius: 4px;
  border: 1px solid #ccc;
`;


Saving Todo items to a database

To save the todo items to a database, you will need to create a backend service that the Next.js app can communicate with. You can use a variety of technologies to build the backend, such as Node.js with Express, Python with Flask or Ruby on Rails.

In your backend service, you will need to create a REST API that the frontend can send requests to for creating, reading, updating, and deleting todo items.

Then you need to call the API in the TodoPage component’s functions like addTodo, deleteTodo to perform the CRUD operations on todo items.

Additionally, you can also use a library like axios or fetch to communicate with the backend service.

In summary, creating a Todo application using Next.js is a straightforward process, but you can also add further functionality like styles, routing, and saving the data to a database. It’s a great way to learn more about building web applications with React and Next.js and you can use the concepts you learn to build more advanced applications in the future.

Difference between constructor and ngOnInit

The Constructor is a default method of the class that is executed when the class is instantiated and ensures proper initialisation of fields in the class and its subclasses. Angular, or better Dependency Injector (DI), analyses the constructor parameters and when it creates a new instance by calling new MyClass() it tries to find providers that match the types of the constructor parameters, resolves them and passes them to the constructor like

new MyClass(someArg);

ngOnInit is a life cycle hook called by Angular to indicate that Angular is done creating the component.

We have to import OnInit like this in order to use it (actually implementing OnInit is not mandatory but considered good practice):

import { Component, OnInit } from '@angular/core';

then to make use of the method OnInit, we have to implement the class like this:

export class App implements OnInit {
constructor() {
// Called first time before the ngOnInit()
}

ngOnInit() {
// Called after the constructor and called after the first ngOnChanges()
}
}

Implement this interface to execute custom initialization logic after your directive’s data-bound properties have been initialized. ngOnInit is called right after the directive’s data-bound properties have been checked for the first time, and before any of its children have been checked. It is invoked only once when the directive is instantiated.

Mostly we use ngOnInit for all the initialisation/declaration and avoid stuff to work in the constructor. The constructor should only be used to initialise class members but shouldn’t do actual “work”.

So you should use constructor() to setup Dependency Injection and not much else. ngOnInit() is better place to “start” – it’s where/when components’ bindings are resolved.