Introduction

Todo app is a simple web app that can get you started with React. React makes it easy to accomplish our task.

Prerequisites

• Basic knowledge of React.

• Basic knowledge of React Hooks.

• Basic knowledge of HTML, CSS, and JavaScript.

Let's start by Creating a React app with the following command. For this example, we will be using the Vite to create the Todo React app

npm create vite@latest todo --tempalate react-swc-ts

Navigate into the directory and install the dependencies.

cd todo && npm i && npm run dev

Now we can see the starter for a Vite React project. Edit the src/App.tsx page to get started.

Initially, create a component for the Input so that we can reuse it across the App.

//components/Input/Input.tsx

import { ComponentPropsWithoutRef } from "react";
import "./styles.css";

interface IInput extends ComponentPropsWithoutRef<"fieldset"> {
  inputProps: ComponentPropsWithoutRef<"input">;
}

export default function Input({ inputProps }: IInput) {
  return (
    <fieldset className="input__container">
      <label htmlFor="todo" className="input__label">
        Add Todo
      </label>
      <input
        {...inputProps}
        type="text"
        name="todo"
        id="todo"
        className="input__input"
      />
    </fieldset>
  );
}

Add the styles for it.

//components/Input/styles.css

.input__container {
  display: flex;
  flex-direction: column;
  gap: 0.25rem;
  border: none;
}
.input__label {
  font-size: 1rem;
  font-weight: 700;
}
.input__input {
  padding: 0.5rem 1rem;
  border-radius: 1rem;
  border: 1px solid rgba(0, 0, 0, 0.4);
  outline: none;
}

Clear everything in the App.tsx and get started with the code below.

//src/App.tsx

<main className="container">
  <h1 className="title">Todos</h1>
</main>

We can now add a form to our UI to begin adding todos to our application.

  <form onSubmit={handleAddTodo} className="add__todo__form">
   <Input inputProps={{ name: "todo", value: todo, onChange: handleOnChange }} />
   <button type="submit" className="add__todo__button">
    Add
   </button>
  </form>

To update the todos we need to listen for changes in our input. We can save our values from the input in a useState React hook.

const [todo, setTodo] = useState("");

Similarly, add the onChange function to add our todo.

const handleOnChange = (e: ChangeEvent<HTMLInputElement>) => {
    const { value } = e.target;
    setTodo(value);
};

In this function, we listen for changes in the input and append the resulting value to our todo state using setTodo.

Similarly, the form will be submitted to the handleAddTodo function. Here, we prevent the default behavior of the browser and add todos to our setTodos useState hook.

const [todos, setTodos] = useState<{ title: string; completed: boolean }[]>([]);
 
const handleAddTodo = (e: SyntheticEvent) => {
    e.preventDefault();
    setTodos((prev) => [...prev, { title: todo, completed: false }]);
    setTodo("");
  };

Continue by building tabs to view the remaining and completed todos. We can handle the state of our active tab by again using the useState React hook.

const [activeTab, setActiveTab] = useState("Remaining Todos");

We can update the active tab value by listening to a click event in the tabs.

<div className="tabs__container">
   {["Remaining Todos", "Completed Todos"].map((tab) => (
      <button
       key={tab}
       className={`tabs__tab ${
       activeTab === tab ? "tabs__tab__active" : ""
       }`}
       onClick={() => setActiveTab(tab)}
       >
          {tab}{" "}
          {tab === "Remaining Todos"
          ? remainingTodos.length > 0 && `(${remainingTodos.length})`
          : completedTodos.length > 0 && `(${completedTodos.length})`}
       </button>
   ))}
</div>

In the above onClick function we make use of the setActiveTab hook to update our activeTab value.

Now we can memoize our remaining and completed todos.

const remainingTodos = useMemo(() => {
    return todos.filter((todo) => !todo.completed);
}, [todos]);

const completedTodos = useMemo(() => {
    return todos.filter((todo) => todo.completed);
}, [todos]);

Finally, render the list of our todos to the UI. Before, rendering the UI we must also check for the active tab state to get the active tab todos.

<ul className="todos__container">
     {(activeTab === "Remaining Todos"
      ? remainingTodos
      : completedTodos
      ).map((todo) => (
           <li key={todo.title} className="todo__list__item">
             <span className="todo__list__item__input__container">
               <input
                type="checkbox"
                checked={todo.completed}
                name={todo.title}
                onChange={(e) => {
                   setTodos((prev) =>
                     prev.map((t) =>
                       t.title === todo.title
                         ? { ...t, completed: e.target.checked }
                         : t
                     )
                   );
                 }}
                />
               {todo.title}
             </span>
             <DeleteB
              onClick={() => {
              setTodos((prev) => prev.filter((t) => t.title !== todo.title));
              }}
            />
           </li>
     ))}
</ul>

Add styles to the page.

//src/index.css

html,
body,
:root,
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
.title {
  font-size: 2.5rem;
  font-weight: 900;
}
.add__todo__form {
  display: flex;
  align-items: flex-end;
  gap: 1rem;
}
.add__todo__button {
  padding: 0.5rem 1rem;
  border-radius: 1.5rem;
  border: none;
  outline: none;
}
.container {
  width: 25rem;
  position: absolute;
  top: 25%;
  left: calc(50% - 10rem);
  display: flex;
  flex-direction: column;
  gap: 1.25rem;
  padding: 2rem 2.5rem;
  border-radius: 2rem;
  border: 1px solid rgb(58, 40, 216);
}
.todo__list__item {
  list-style-type: none;
  display: flex;
  gap: 0.25rem;
  align-items: center;
  justify-content: space-between;
  padding: 0.25rem 1rem;
}
.tabs__container {
  display: flex;
  align-items: center;
  gap: 1rem;
}
.tabs__tab {
  white-space: nowrap;
  font-size: 1rem;
  font-weight: 500;
  outline: none;
  border: none;
  background: transparent;
}
.tabs__tab__active {
  border-bottom: 1px solid blue;
}
.todos__container {
  height: 20rem;
  overflow-y: scroll;
}
.todo__list__item__input__container {
  display: flex;
  gap: 0.25rem;
  align-items: center;
}

Conclusion

Here, we created a to-do app in React using Vite and React hooks. You can now further update the UI and add additional functionalities to your to-do app to make it even better.

Introduction

Let's start by cloning our already made todo app. We will be testing the crud function and also checking for UI updates. Vitest is easy to get started with. Just follow along and you will begin testing your apps soon.

Add Vitest,jsdom and necessary testing libraries for UI testing to get started.

npm i -D vitest @testing-library/jest-dom @testing-library/user-event @types/jest @vitest/ui jsdom

You can additionally add the following scripts to package .json

"scripts": {
     "test": "vitest",
     "test:ui": "vitest --ui",
     "coverage": "vitest run --coverage"
}

Before testing our application, we need to set up some files to get started. Start by creating a new file test-utils that will have all the utilities for our tests.

//tests/test-utils.tsx

import { cleanup, render } from "@testing-library/react";
import { afterEach } from "vitest";

afterEach(() => {
  cleanup();
});

function customRender(ui: React.ReactElement, options = {}) {
  return render(ui, {
    // wrap provider(s) here if needed
    wrapper: ({ children }) => children,
    ...options,
  });
}

export * from "@testing-library/react";
export { default as userEvent } from "@testing-library/user-event";
// override render export
export { customRender as render };

//tests/setup.ts

import '@testing-library/jest-dom';

We need now to update our Vite config to include test files.

// vite.config.ts

export default defineConfig({
  plugins: [react()],
  test: {
    globals: true,
    environment: 'jsdom',
    setupFiles: './src/test/setup.ts',
    // you might want to disable it, if you don't have tests that rely on CSS
    // since parsing CSS is slow
    css: true,
  },
})

First, let's start by performing component testing. For this, we can create a test file to test our input component. We can test as many scenarios as we like. Here, we will test if the component is rendered properly and if the input can change values and update as we require. Initially, we will test to see if the component in rendered to the document.

//components/Input/Input.test.tsx

import { render, screen, userEvent } from "../../utils/test-utils";
import Input from "./Input";

test("should render the input component.", () => {
  render(<Input label="Add Todo" inputProps={{}} />);
  expect(screen.getByText(/Add Todo/i)).toBeInTheDocument();
  expect(screen.getByRole("textbox", { name: "Add Todo" })).toBeInTheDocument();
});

First, we render the component making use of @testing-library/react and we will check if the component is rendered. We can additionally check for props and values the input component should have as the props have been passed in. for this we can again make use of helper functions provided by @testing-library/react to get the component properties. Here, we test to see if the input component has the label of "Add Todo" and we also check for the input box having the name 'Add Todo'.

We can now test our input for value changes and updates.

test("should update input value on change.", async () => {
  render(<Input label="Add Todo" inputProps={{}} />);
  const input = screen.getByRole("textbox", { name: "Add Todo" });
  expect(input).toBeInTheDocument();
  await userEvent.type(input, "new todo");
  expect(input).toHaveValue("new todo");
});

Here, we render the input then we check if the input box is present in the document. If the input box check passes we can then type anything we want into the input box. We then check if the input has the same value as we typed.

Now we can test our addtodo functionality in the app. Continue by creating a new file AddTodo.test.tsx . We can begin by checking if the UI for the form is present in the document.

//src/AddTodo.test.tsx

import App from "./App";
import { render, screen, userEvent } from "./utils/test-utils";

test("should render the todo form.", () => {
  render(<App />);
  expect(screen.getByText(/Add Todo/i)).toBeInTheDocument();
  expect(screen.getByRole("textbox", { name: "Add Todo" })).toBeInTheDocument();

  const button = screen.getByRole("button", { name: /add/i });
  expect(button).toBeInTheDocument();
});

Now we can test the functionality of the add todo form. Here, we again test by rendering the App component and then check for the title of the remaining todo in the document. Then we add a new todo to the input and click on the button for adding. We then finally check if the newly added todo is also present in the UI document.

test("should add todo to the remaining todos list.", async () => {
  render(<App />);
  expect(screen.getByText(/Remaining Todos/i)).toBeInTheDocument();

  const input = screen.getByRole("textbox", { name: /add todo/i });
  expect(input).toBeInTheDocument();
  await userEvent.type(input, "new todo");

  const button = screen.getByRole("button", { name: /add/i });
  expect(button).toBeInTheDocument();
  await userEvent.click(button);
  expect(screen.getByText(/new todo/i)).toBeInTheDocument();
});

Conclusion

We successfully tested different scenarios for the todo app. We also made it possible to pass all the tests. Implement similarly in your apps now.

Introduction

Pattern problems are great for practicing loops and logical thinking in programming. We will discuss and try out some of the basic pattern problems.

• Right Triangle

  for (let i = 0; i < 5; i++) {
    let pattern = "";
    for (let j = 0; j < i; j++) {
      pattern += "*";
    }
    console.log(pattern);
  }

  Output:

  *
  **
  ***
  ****
  *****

• Left Triangle

  for (let i = 5; i > 0; i--) {
    let pattern = "";
    for (let j = i; j > 0; j--) {
      pattern += "*";
    }
    console.log(pattern);
  }

  Output:

  *****
  ****
  ***
  **
  *

• Pyramid

  const n = 5;
  for (let i = 0; i < n; i++) {
    let pattern = "";
    for (let j = 0; j < n - i; j++) {
      pattern += " ";
    }
  
    for (let k = 0; k < i; k++) {
      pattern += "*";
    }
    for (let l = i - 1; l > 0; l--) {
      pattern += "*";
    }
  
    console.log(pattern);
  }

  Output:

      *
     ***
    *****
   *******

• Diamond

  const n = 5;
  
  for (let i = 1; i <= n; i++) {
    let pattern = "";
    for (let j = 1; j <= n - i; j++) {
      pattern += " ";
    }
    for (let k = 1; k <= 2 * i - 1; k++) {
      pattern += "*";
    }
    console.log(pattern);
  }
  
  for (let i = n - 1; i >= 1; i--) {
    let pattern = "";
    for (let j = 1; j <= n - i; j++) {
      pattern += " ";
    }
    for (let k = 1; k <= 2 * i - 1; k++) {
      pattern += "*";
    }
    console.log(pattern);
  }

  Output:

      *
     ***
    *****
   *******
  *********
   *******
    *****
     ***
      *

The useWindowSize hook in react is very useful when you require javascript to get the size of the device and render the contents as required. It very useful when working with various sizes of devices. It can be useful when working with responsive designs. The following code demonstrates how one can implement the useWindowSize hook in their next project.

import { useEffect, useState } from "react"; 

export default function useWindowSize() { 
   // state of the window 
   const [windowSize, setWindowSize] = useState({ width: 0, height: 0, });

   // function to handle window resizing. 
   const resizeWindow = () => { 
      setWindowSize({ width: window.innerWidth, height: window.innerHeight }); 
   };

   useEffect(() => { 
      resizeWindow();

      // event listener for handling window size change. 
      window.addEventListener("resize", resizeWindow);

      // cleanup the side effects
      return () => window.removeEventListener("resize", resizeWindow);
   }, []); 

   // return window size
   return windowSize; 
}

You can use the hook in your required tsx/jsx file as follows:

import useWindowSize from "./useWindowSize";

export default function MyResponsiveComponent(){
   const {width, height} = useWindowSize()

   if (width > 375) {
      return <TabletView/>
   } else if (width > 1200) {
      return <DesktopView/>
   } else if (height > 1000) {
      return <LargeHeightView/>
   } else {
      return <MobileView/>
   }
}

You can use the above code or modify to your own use in react to handle contents in various devices.