ReactJS

Getting Started with React and TypeScript

Published Jan 27, 2021

Updated Feb 14, 2023

7 min read

This article was written over 18 months ago and may contain information that is out of date. Some content may be relevant but please refer to the relevant official documentation or available resources for the latest information.

Getting Started with React and TypeScript

React and TypeScript makes for a fantastic combination when it comes to developing web sites and web applications. With React's focus on creating a fantastic user interface and TypeScript's ability to type check our code, it's never been easier to sanely develop a fantastic user experience.

Prerequisites

Before getting started, you'll need NodeJS and NPM installed. Go here to find instructions on how to install it on your computer.

You should also have a bit of knowledge in using React. If not, I highly recommend getting started learning React using vanilla JavaScript.

Create React App

Facebook's Create-React-App is a preview of the wonderful development experience React has to offer. It will enable us to start writing code immediately.

Check out their documentation here if you have any questions or want to dive in a touch deeper on how the tool works.

In summary, Create-React-App will set up a complete development environment for us. It will configure and conceal build tool configurations for us so that all we need to focus on is our code. Here is some of the tooling that CRA (create-react-app) sets up for us:

Let's use this tool now to create our TypeScript/React development environment. Use the following command to generate a new Typescript React App.

npx create-react-app my-app --template typescript

If you use yarn, use the following command:

yarn create react-app my-app --template typescript

After the tool has finished running, switch directories into my-app run the command npm start to spin up your development environment. Once it's done loading, we should see localhost:3000 open up.

Folder Structure

Create-react-app scaffolds out the folder structure of your app for us, minimizing the amount of code you need to write to go from idea to production.

Here are some important files to take note of:

public/index.html - This is the HTML file that consumes the bundle generated by Create-React-App's hidden tooling.
src/index.tsx - This is the TypeScript entry point file. All of the project's dependencies are mapped out by Webpack (all set up for us invisibly by CRA) using this file. The bundle generated is injected into public/index.html. This file has a few responsibilities. The most important are:
- import our main React component
- Render that App component to the DOM using ReactDom.render()
src/App.tsx - This is our main React Component. The .tsx extension tells us that the file uses both TypeScript and JSX. This is the main component in our app which is rendered to the DOM by ReactDOM. We'll spend most of our time in this file getting the hang of writing React code using TypeScript.
tsconfig.json - This is the TypeScript configuration file. This file was generated for us by Create-React-App and we can freely edit this configuration to best suit our needs.

Hello, World - With TypeScript and React

Let's get to coding.

To keep things organized, make a new folder src/components and create our new component, src/components/HelloWorld.tsx. In this file, we'll write just 2 lines of code:

const HelloWorld = () => <h1>Hello, World!</h1>
export default HelloWorld

The first line defines our new component. It's simply a function that returns some JSX. In this case, it's our "Hello, World!" heading tag. The second line exports the component, allowing other modules to import it.

To import and use this component, load up src/App.tsx and do the following:

Include import HelloWorld from './components/HelloWorld' at the very top of the file to import the component
Use the component by having the App component return some JSX which includes <HelloWorld />.

After some refactoring, your App.tsx might look something like this:

import './App.css';
import HelloWorld from './components/HelloWorld'

const App = () => {
  return (
    <div className="App">
      <HelloWorld />
    </div>
  );
}

export default App;

In the above example, I've left the default styles, imported our HelloWorld component, and refactored the JSX which is returned by App so it includes <HelloWorld />.

Adding a bit of TypeScript

Let's increase the safety of our code by using some TypeScript features.

This is what our src/components/HelloWorld.tsx looks like right now:

const HelloWorld = () => <h1>Hello, World!</h1>
export default HelloWorld

A huge benefit of TypeScript is that it can help us catch errors before you run your code instead of at run-time. Let's introduce a bug to our code:

Refactor our HelloWorld component so it looks like this:

const HelloWorld = () => "Hello, World!"
export default HelloWorld

This is valid JavaScript, but not valid React. A functional component must return JSX (or null). It can't just return a string. We're made aware of this error when Create-React-App tries to build our code.

Let's refactor our code to use some TypeScript features so our editor notices the error:

import { FC } from 'react'
const HelloWorld: FC = () => "Hello, World!"
export default HelloWorld

The import statement imports the FunctionComponent type FC, and allows us to type our functional component to ensure it returns valid JSX. By typing the function, our editor can now immediately show us our error. Click here for more information on typing functions in TypeScript.

TypeScript is explicitly telling us that we can't assign a return type of string to our functional component. Now that TypeScript has shown us this error, let's correct it.

import { FC } from 'react'
const HelloWorld: FC = () => <h1>Hello, World!</h1>
export default HelloWorld

By fixing our function and returning JSX, HelloWorld now passes TypeScript's type checks and no error is thrown. As a result, our project builds and works once more.

Benefits of TypeScript

As shown in the previous example, TypeScript can help us catch errors before we even leave our code editor. This results in faster development since TypeScript will be actively debugging your code as you write. Better to catch silly errors immediately than insanity-inducing errors during run-time.

Let's show another example of how enforcing types can help us catch errors early.

We'll create a new React component, List. This new component will take an array of string data as a prop and return some JSX which renders a <ul> tag and iterate over the list of data, rendering an <li> for each piece of data.

Here is what my version of this component could look like with more type safety from TypeScript included.

src/components/List.tsx

import { FC } from 'react'

const List: FC<{ data: string[] }> = ({ data }) => (
  <ul>
    {data.map(item => <li>{item}</li>)}
  </ul>
)

export default List

Just like our previous example, we import FC from react and use it to type our function. What we're also doing is defining a type for our data prop. In this example, we are saying that data is an array of strings. Notice how self-documenting that is. This is a huge benefit of TypeScript.

Now let's insert this component into src/App.tsx, pass into it an array of data, and sprinkle in a bit more TypeScript.

src/App.tsx

import './App.css';
import { FC } from 'react'
import HelloWorld from './components/HelloWorld'
import List from './components/List'

const avengers = [
  'Captain America',
  'Iron Man',
  'Black Widow',
  'Thor',
  'Hawkeye',
]

const App: FC = () => {
  return (
    <div className="App">
      <HelloWorld />
      <List data={avengers} />
    </div>
  );
}

export default App;

We created an avengers array, with 5 members of the Avengers team. We then passed in this list of data as a property to List. This example works because we defined List to accept an array of strings. Let's trigger a TypeScript error and send it a more varied array.

import './App.css';
import { FC } from 'react'
import HelloWorld from './components/HelloWorld'
import List from './components/List'

const avengers = [
  'Captain America',
  'Iron Man',
  'Black Widow',
  'Thor',
  'Hawkeye',
  {
    name: 'Vision',
  },
  {
    name: 'Hulk',
    color: 'green',
  },
]

const App: FC = () => {
  return (
    <div className="App">
      <HelloWorld />
      <List data={avengers} />
    </div>
  );
}

export default App;

We added 2 new heroes to the avengers array, Vision and the Hulk, but we added them as objects, not as strings. This causes TypeScript to throw an error.

TypeScript is telling us that our data doesn't fit the definition of the data prop. It even points out to us exactly where this prop is defined. Let's assume that we should be sending an array of objects instead of strings. Let's refactor our files so everything works again.

src/App.tsx

import './App.css';
import { FC } from 'react'
import HelloWorld from './components/HelloWorld'
import List from './components/List'

const avengers = [
  { name: 'Captain America' },
  { name: 'Iron Man' },
  { name: 'Black Widow' },
  { name: 'Thor' },
  { name: 'Hawkeye' },
  { name: 'Vision' },
  { name: 'Hulk' },
]

const App: FC = () => {
  return (
    <div className="App">
      <HelloWorld />
      <List data={avengers} />
    </div>
  );
}

export default App;

src/components/List.tsx

import { FC } from 'react'

const List: FC<{ data: { name: string }[] }> = ({ data }) => (
  <ul>
    {data.map(({ name }) => <li>{name}</li>)}
  </ul>
)

export default List

We changed our List component definition and explicitly typed the data prop to be an array of objects containing a string type name property. By explicitly typing our data prop, we know its exact shape and can catch if we send this component any prop that is shaped differently than this.

Conclusion

By adding a type layer over JavaScript, TypeScript successfully saves developers time and frustration, even giving us a hand in self-documenting our code. While there surely is much more left to learn in typing your React applications, this should be a good platform to begin wading into the deep end of the pool, so to speak.

Happy coding!

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About the author(s)

Matthew Pagan
@mastapegs @mastapegs

Improving INP in React and Next.js

Improving INP in React and Next.js In one of my previous articles, I've explained what INP is, how it works, and how it may affect your website. I also promised you to follow up with more concrete advice on how to improve your INP in your favorite framework. This is the follow-up article, where I'll focus on how to improve your INP score in React and Next.js. How to prepare for INP in React and Next.js? The first thing to do is to ensure you're using the latest version of React. The React team has been working on making React more INP-friendly and has already made some improvements in the latest versions. To enhance your INP score, consider fully taking advantage of new features introduced in React 18, such as Concurrent Rendering, Automatic Batching, and Selective Hydration. However, there are also some general areas to focus on, such as SSR and SSG in Next.js, Web Workers, or optimizing your hooks and state management. Concurrent Rendering The Concurrent Mode in React uses an algorithm that breaks rendering down into so-called "fiber nodes" and schedules the renders based on their expiration and priority. This effectively allows the user to interact with the page while the rendering is still in progress. In previous React versions, all updates, such as setState calls were treated as "urgent" and once the re-render had started, there was no way to interrupt it. Concurrent Mode changes this by being able to prioritize the updates and interrupt a non-blocking state update started with startTransition. For a simple explanation of concurrency in React, you can check out Dan Abramov's explanation. As part of the Concurrent Mode, React introduced several lifecycle methods that allow you to prioritize the rendering of certain parts of your UI, such as: - useTransition hook that allows you to update the state without blocking the UI, - useDeferredValue hook that allows you to defer the rendering of certain parts of your UI, - startTransition API that, similarly to the useTransition hook lets you mark a state update as non-blocking. It lacks, however, an indication of whether it's still pending. Automatic Batching Introduced in React 18, Automatic Batching reduces the number of re-renders that happen on state changes even when they happen outside of event handlers, e.g. in a setTimeout or Promise callback. This feature comes out of the box and you don't have to do anything to enable it, and it makes a great argument for upgrading to React 18. Selective Hydration Selective Hydration allows you to take hydration off the main thread by wrapping your components in a Suspense boundary. This way, components can become interactive faster as the browser can do other work on the main thread while the hydration is happening. To fully take advantage of selective hydration, consider the following: - Prioritizing Above-the-Fold Content: Use Suspense boundaries strategically around any parts of your application that may take the server longer to deliver to ensure they don’t block critical content from becoming interactive as soon as possible. - Hydration on Interaction: Implementing hydration upon user interaction for non-critical components can drastically reduce the main thread's workload, enhancing INP. Vercel even has a small case study showing how using selective hydration improved the performance of a Next.js site. Server-Side Rendering (SSR) and Static Site Generation (SSG) in Next.js Not everything has to run client-side. Next.js excels in SSR and SSG capabilities, which can significantly impact INP by delivering content to users faster. Optimizing SSR with techniques like incremental static regeneration (ISR) or leveraging SSG for static pages ensures that users can interact with content faster, improving the perceived performance. Workers Offloading heavy computations to Web Workers can free up the main thread, enhancing the responsiveness of React and Next.js applications. This strategy is especially useful when dealing with third-party scripts. Offloading such scripts in Next.js can be easily done by specifying the "worker" strategy on your Script component. Be aware that this feature is not yet stable and does not work with the app directory, though. If you want to take things one step further, you could use Partytown, which helps you offload any resource-intensive scripts to Web Workers. It comes with a React component that you can use to wrap your third-party scripts and offload them to a Web Worker, and it's compatible with Next.js as well. Hooks and State Management State management in React applications can easily get out of hand, leading to unnecessary re-renders and effectively an increased INP. Sometimes, using a state management library like Redux or MobX can help you consolidate your state and reduce the number of re-renders. However, they are not silver bullets and can also introduce performance issues if not used properly. If you are dealing with a lot of re-renders due to prop changes, make sure you are leveraging memoization. As of now, you may need to work with useMemo and useCallback hooks to memoize your values and functions, respectively. The upcoming React 19’s Forget Compiler, however, will apparently memoize everything under the hood, making these hooks obsolete. Using memoization properly can help you reduce the number of re-renders and improve your INP. To investigate your hook dependencies and re-renders, you can leverage React Developer Tools or use this handy helper hook I found on the internet to trace your re-renders: ` Conclusion Improving INP in React and Next.js is not easy and can require much investigation and fine-tuning. Still, it's worth doing to avoid being penalized by Google in its search results and provide a better experience for your users. Adopting React 18's new features, leveraging SSR and SSG in Next.js, utilizing Web Workers, and optimizing hooks and state management can significantly boost your INP score and deliver a faster application to your users. Remember, INP is just one among many performance metrics emphasizing the need for a comprehensive approach to performance optimization...

Apr 19, 2024

5 mins

Web PerformanceReactNextJSJavaScript

Why is My React Reducer Called Twice and What the Heck is a Pure Function?

Why is My React Reducer Called Twice and What the Heck is a Pure Function? In a recent project, we encountered an interesting issue: our React reducer was dispatching twice, producing incorrect values, such as incrementing a number in increments of two. We hopped on a pairing session and started debugging. Eventually, we got to the root of the problem and learned the importance of pure functions in functional programming. This article will explain why our reducer was being dispatched twice, what pure functions are, and how React's strict mode helped us identify a bug in our code. The Issue We noticed that our useReducer hook was causing the reducer function to be called twice for every action dispatched. Initially, we were confused about this behavior and thought it might be a bug in React. Additionally, we had one of the dispatches inside a useEffect, which caused it to be called twice due to React strict mode, effectively firing the reducer four times and further complicating our debugging process. However, we knew that React's strict mode caused useEffect to be called twice, so it didn't take very long to realize that the issue was not with React but with how we had implemented our reducer function. React Strict Mode React's strict mode is a tool for highlighting potential problems in an application. It intentionally double-invokes specific lifecycle methods and hooks (like useReducer and useEffect) to help developers identify side effects. This behavior exposed our issue, as we had reducers that were not pure functions. What is a Pure Function? A pure function is a function that: - Is deterministic: Given the same input, always returns the same output. - Does Not Have Side Effects: Does not alter any external state or have observable interactions with the outside world. In the context of a reducer, this means the function should not: - Modify its arguments - Perform any I/O operations (like network requests or logging) - Generate random numbers - Depend on any external state Pure functions are predictable and testable. They help prevent bugs and make code easier to reason about. In the context of React, pure functions are essential for reducers because they ensure that the state transitions are predictable and consistent. The Root Cause: Impure Reducers Our reducers were not pure functions. They were altering external state and had side effects, which caused inconsistent behavior when React's strict mode double-invoked them. This led to unexpected results and made debugging more difficult. The Solution: Make Reducers Pure To resolve this issue, we refactored our reducers to ensure they were pure functions. Here's an extended example of how we transformed an impure reducer into a pure one in a more complex scenario involving a task management application. Let's start with the initial state and action types: ` And here's the impure reducer similar to what we had initially: ` This reducer is impure because it directly modifies the state object, which is a side effect. To make it pure, we must create a new state object for every action and return it without modifying the original state. Here's the refactored pure reducer: ` Key Changes: - Direct State Modification: In the impure reducer, the state is directly modified (e.g., state.tasks.push(action.payload)). This causes side effects and violates the principles of pure functions. - Side Effects: The impure reducer included side effects such as logging and direct state changes. The pure reducer eliminates these side effects, ensuring consistent and predictable behavior. I've created an interactive example to demonstrate the difference between impure and pure reducers in a React application. Despite the RESET_TASKS action being implemented similarly in both reducers, you'll notice that the impure reducer does not reset the tasks correctly. This problem happens because the impure reducer directly modifies the state, leading to unexpected behavior. Check out the embedded StackBlitz example below: Conclusion Our experience with the reducer dispatching twice was a valuable lesson in the importance of pure functions in React. Thanks to React's strict mode, we identified and fixed impure reducers, leading to more predictable and maintainable code. If you encounter similar issues, ensure your reducers are pure functions and leverage React strict mode to catch potential problems early in development. By embracing functional programming principles, you can write cleaner, more reliable code that is easier to debug and maintain....

Jun 14, 2024

3 mins

React

How to make Videos with React using Remotion

How to make Videos with React using Remotion We've written a blog post discussing how React truly is a "Learn Once, Write Anywhere" library. In that article, we talked about how we aren't limited to rendering React components to the DOM. In this post, we'll discuss how we can leverage our knowledge of developing React components and create Videos, using Remotion. If you already know [React] and follow along with this post, you'll walk away with a custom .mp4 video of you're own creation, and the knowledge of how to customize it to you're heart's content. Remotion Remotion is a suite of libraries for creating videos programmatically with React. Just like react-dom is used to provide an interface between React components, and rendering to the DOM, Remotion is used to provide an interface between React and rendering to Video. > If you know React, you can make videos. > -- Remotion Documentation This is exciting because it allows developers to re-use their knowledge of the React library for yet another purpose. Let's dive in and see how we can start rendering some videos! Initializing a Remotion Video Project Creating a new Remotion video is as easy as a 1 line command: npm init video Running this command gives the user access to a few default templates for Remotion video development: - Hello World - Blank - Hello World (Vanilla Javascript) - React Three Fiber - Still Images - Text to Speech The Hello World templates are fantastic places to go if you are a hands-on learner and like playing around with your code in a live dev environment. They're how I learned to use Remotion. They're packed with such great logic, that I'd encourage you to run a template before moving on and exploring them a bit to see how things are laid out. That being said, I want to go over things rather slowly, so I'm going to create a repo from the Blank template, add a few development features (linting, husky, prettier, etc), and use that as a starting point. If you want to develop with these features and want a similar starting point, clone the repo here and you can see every commit from beginning to end. This is the exact commit after I finished installing linting to the Blank template. The Blank Remotion Template If you cloned the repo I mentioned above, you'll be working in the Blank template, with a few additional dev features. The main 2 files are: - src\index.tsx: This is similar to the index file of a regular create-react-app. It uses a render function to take a React component, and render it to the desired output, in this case, a .mp4 video. We won't be looking in here. - src\Video.tsx: This is the main entry point of our video. Think of this as the App component in a create-react-app project. It's here that we layer together React components to create our Remotion video. This is where we will start to focus our attention. The Composition component The entry point file Video.tsx introduces us to our first Remotion component, Composition. ` We can see this component in action by running npm start and checkouting out our development environment: The Remotion development environment has 4 important sections: - Compositions: The left main column. This is a list of all defined Composition components in Video.tsx. The Blank template defines a single Composition, with an id == 'Empty' - Scenes: The bottom left column. We haven't talked about scenes yet... - Composition Render: The main dev zone. This is the development render of the currently selected Composition. - Composition Timeline: This is a timeline of scenes rendered in the currently selected Composition. The Composition component has a few important properties: - id: This is the name given to the Composition, used to identify the component in the development environment. - component: This is the component that the Composition renders. Different compositions can render the same component, for responsiveness for example. - durationInFrames & fps: A Composition is not defined by how long it is in time, but by how many frames it is made up of, and how fast those frames are rendered. - width & height: Together, these define the aspect ratio of our video. You could define an HD Composition with a 1920/1080 width/height, or a square still from a single frame of a Component with a 200/200 width/height for example. - defaultProps: This is the props object passed into the component when the Composition is rendered. This repository defines a super small empty component as the component-to-render for the Empty composition. Let's rename our component to HelloWorld, and create a full-fledged component to render. We'll render a simple, 4-second video, of the text "Hello, World!", in high definition, at 60fps. src/Video.tsx ` src/components/HelloWorld.tsx ` To render this to .mp4 you need to have ffmpeg installed. Adjust the package.json build command and instruct the CLI to render our HelloWorld composition, and run npm run build to create our first video! Here's a link to what this would render. It's nothing crazy, but with previous React knowledge, and with the help of Remotion, we have created a 4 second long, 60fps, 4K video! Simple animations with interpolate Rendering some static text to video doesn't make for an exciting video, so let's learn how to reach into the state of the application, and adjust the style of our text, depending on the current frame. Here are the 2 hooks we'll use to accomplish this: - useCurrentFrame: This hook returns the current frame number. - interpolate: This hook helps the user change values throughout several frames. It takes in 3 arguments, the current frame (from useCurrentFrame), a tuple designating the start and end frame for the interpolation, and another tuple defining the start and end values for the frame duration. Using these 2 hooks, we can define what the opacity of our text should be, as a function of the current frame: ` Here's a link to what this would render. We aren't rendering static text anymore. Now we have a real video! The Sequence component Videos can be made up of MANY moving parts though. Our current video only has 1 moving part, but let's add some complexity to the video and split this into 2 parts. To do this, we need to take advantage of the Sequence component. > Using a Sequence, you can time-shift certain parts of your animation and therefore make them more reusable. Sequences are also shown in the timeline and help you visually understand the structure of your video. > -- Remotion Docs We can use sequences to help us break apart our logic even further, and we can also view these sequences on our composition timeline. Here are some important props for the Sequence component: - from (required, number): The frame that the Sequence children start at. The initial frame for them is 0. - durationInFrames (optional, default: Infinity): This is how many frames a sequence is displayed. - name (optional): Name your sequences to label them in the development environment. - layout (optional, default: 'absolute-fill'): Sequences are positioned absolutely initially, use this to handle layout manually. Let's animate our "Hello, World!" a bit more: src/components/HelloWorld.tsx ` With a few sequences, we are now separating our animations, and labeling them in our dev environment. Here is the render uploaded to YouTube. Putting the 'World' in 'Hello, World!' Being able to render text is amazing, but in the animation world, models aren't drawn manually with code. Instead, they're generated using software, such as Blender for example. One of the tools we can render with using Remotion is React Three Fiber. Just like Remotion lets us render to a Video format, React Three Fiber allows us to render React components into ThreeJS, a WebGL library. With a bit of React Three Fiber logic and a publicly available model of our planet, we can put the 'World' in 'Hello, World!' Hello, World! Going into how to work with React Three Fiber is a bit out of the scope of this post, but I wanted to show just what the developer is capable of with Remotion, and rendering a spinning planet with JSX is pretty amazing. src/components/HelloWorld.tsx ` Conclusion React truly is a "Learn Once, Write Anywhere" language. The DOM is nowhere close to the only render target React is capable of. With Remotion, we've learned how to slap together some JSX and hooks, and render actual videos, programmatically. Feel free to clone the repo and play around with the logic. If you've followed along with this post, you can now proudly state that you can literally render "Hello, World!" with React!...

Oct 15, 2021

7 mins

React

Increasing development velocity with Cursor

If you’re a developer, you’ve probably heard of Cursor by now and have either tried it out or are just curious to learn more about it. Cursor is a fork of VSCode with a ton of powerful AI/LLM-powered features added on. For around $20/month, I think it’s the best value in the AI coding space. Tech giants like Shopify and smaller companies like This Dot Labs have purchased Cursor subscriptions for their developers with the goal of increased productivity. I have been using Cursor heavily for a few months now and am excited to share how it’s impacted me personally. In this post, we will cover some of the basic features, use cases, and I’ll share some tips and tricks I’ve learned along the way. If you love coding and building like me, I hope this post will help you unleash some of the superpowers Cursor’s AI coding features make possible. Let’s jump right in! Cursor 101 The core tools of the Cursor tool belt are Autocomplete, Ask, and Agent. Feature: Autocomplete The first thing that got me hooked was Autocomplete. It just worked so much better than the tools I had used previously, like GitHub Copilot. It was quicker and smarter, and I could immediately notice the amount of keystrokes that it was saving me. This feature is great because it doesn’t really require any work or skilled prompting from the user. There are a couple of tricks for getting a little bit more out of it that I will share later, but for now, just enjoy the ride! Feature: Ask If you’ve interacted with AI/LLMs before, like ChatGPT - this is what the Ask feature is. It’s just a chat feature you can easily provide context to from your code base and choose which Model to chat with. This feature is best suited for just asking more general questions that you might have queried Google or Stack Overflow for in the past. It’s also good for planning how to implement a feature you’re working on. After chatting or planning, you can switch directly to Agent mode to pick up and take action on something you were cooking up in Ask mode. Here’s an example of planning a simple tic-tac-toe game implementation using the Ask feature: Feature: Agent Agent mode lets the AI model take the wheel and write code, make edits, or take other similar actions on your code base. The goal is that you can write prompts and give instructions, and the Agent can generate the code and build features or even entire applications for you. With great power comes great responsibility. Agents are a feature where the more you put into them, the more you get out. The more skilled you become in using them by providing better prompts and including the right context, you will continue to get better results. The AI doesn’t always get it right, but the fact that the models and the users are both getting better is exciting. Throughout this post, I will share the best use cases, tips, and tricks I have found using Cursor Agent. Here’s an example using the Agent to execute the implementation details of the tic-tac-toe game we planned using Ask: Core Concept: Context After understanding the features and the basics of prompting, context is the most important thing for getting the best results out of Cursor. In Cursor and in general, whenever you’re prompting a chat or an agent, you want to make sure that it has all the relevant information that it needs to provide an answer or result. Cursor, by default, always has some context of your code. It indexes your code base and usually keeps the open buffer in the context window at the very least. At the top left of the Ask or Agent panel, there is an @ button, and next to that are badges for all the current items that have been explicitly added to the context for the current session. The @ button has a dropdown that allows you to add files, folders, web links, past chats, git commits, and more to the context. Before you prompt, always make sure you add the relevant content it needs as context so that it has everything it needs to provide the best response. Settings and Rules Cursor has its own settings page, which you can access through Cursor → Settings → Cursor Settings. This is where you log in to your account, manage various features, and enable or disable models. In the General section, there is an option for Privacy Mode. This is one setting in particular I recommend enabling. Aside from that, just explore around and see what’s available. Models The model you use is just as important as your prompt and the context that you provide. Models are the underlying AI/LLM used to process your input. The most well-known is GPT-4o, the default model for ChatGPT. There are a lot of different models available, and Cursor provides access to most of them out of the box. Model pricing A lot of the most common models, like GPT-4o or Sonnet 3.5/3.7, are included in your Cursor subscription. Some models like o1 and Sonnet 3.7 MAX are considered premium models, and you will be billed for usage for these. Be sure to pay attention to which models you are using so you don’t get any surprise bills. Choosing a Model Some models are better suited for certain tasks than others. You can configure which models are enabled in the Cursor Settings. If you are planning out a big feature or trying to solve some complex logic issue, you may want to use one of the thinking models, like o1, o3-mini, or Deep Seek R1. For most coding tasks and as a good default, I recommend using Sonnet 3.5 or 3.7. The great thing about Cursor is that you have the options available right in your editor. The most important piece of advice that I can give in this post is to keep trying things out and experimenting. Try out different models for different tasks, get a feel for it, and find what works for you. Use cases Agents and LLM models are still far from perfect. That being said, there are already a lot of tasks they are very good at. The more effective you are with these tools, the more you will be able to get done in a shorter amount of time. Generating test cases Have some code that you would like unit tested? Cursor is very good at generating test cases and assertions for your code. The fewer barriers there are to testing a piece of code, the better the result you will get. So, try your best to write code that is easily testable! If testing the code requires some mocks or other pieces to work, do your best to provide it the context and instructions it needs before writing the tests. Always review the test cases! There could be errors or test cases that don’t make sense. Most of the time, it will get you pretty close to where you want to be. Here’s an example of using the Agent mode to install packages for testing and generate unit tests for the tic-tac-toe game logic: Generating documentation This is another thing we know AI models are good at - summarizing large chunks of information. Make sure it has the context of whatever you want to document. This one, in particular, is really great because historically, keeping documentation up to date is a rare and challenging practice. Here’s an example of using the Agent mode to generate documentation for the tic-tac-toe game: Code review There are a lot of up-and-coming tools outside of Cursor that can handle this. For example, GitHub now has Copilot integrated in pull requests for code reviews. It’s never a bad idea to have whatever change set you’re looking to commit reviewed and inspected before pushing it up to the remote, though. You can provide your unstaged changes or even specific commits as context to a Cursor Ask or Agent prompt. Getting up to speed in a new code base Being able to query a codebase with the power of LLM’s is truly fantastic. It can be a great help to get up to speed in a large new codebase quickly. Some example prompts: > Please provide an overview of this project and how to get started developing with it > I need to make some changes to the way that notifications are grouped in the UI, please provide a detailed analysis and pseudo code outlining how the grouping algorithm works If you have a question about the code base, ask Cursor! Refactoring Refactoring code in a code base is a much quicker process in Cursor. You can execute refactors depending on their scope in a couple of distinct ways. For refactors that don’t span a lot of files or are less complex, you can probably get away with just using the autocomplete. For example, if you make a change to something in a file and there are several instances of the same pattern following, the autocomplete will quickly pick up on this and help you tab through the changes. If you switch to another file, this information will still be in context and can be continued most of the time. For larger refactors spanning several files, using the Agent feature will most likely be the quickest way to get it done. Add all the files you plan to make changes to the Agent tab’s context window. Provide specific instructions and/or a basic example of how to execute the refactor. Let the Agent work, if it doesn’t get it exactly right initially, you can always give it corrections in a follow-up prompt. Generating new code/features This is the big promise of AI agents and the one with the most room for mixed results. My main recommendation here is to keep experimenting. Keep learning to prompt more effectively, compare results from different models, and pay attention to the results you get from each use case. I personally get the best results building new features in small, focused chunks of work. It can also be helpful to have a dialog with the Ask feature first to plan out the feature's details that the Agent can follow up on and implement. If there are existing patterns in your codebase for accomplishing certain things, provide this information in your prompts and make sure to add the relevant code to the context. For example, if you’re adding a new form to the web page and you have other similar forms that handle validation and making back-end calls in the same way, Cursor can base the code for the new feature on this. Example prompt: Generate a form for creating a new post, follow similar patterns from the create user profile form, and look to the post schema for the fields that should be included. Remember that you can always follow up with additional prompts if you aren’t quite happy with the results of the first.. If the results are close but need to be adjusted in some way, let the agent know in the next prompt. You may find that for some things, it just doesn’t do well yet. Mentally note these things and try to get to a place where you can intuit when to reach for the Agent feature or just write some of the code the old-fashioned way. Tips and tricks The more you use Cursor, the more you will find little ways to get more out of it. Here are some of the tips and patterns that I find particularly useful in my day-to-day work. Generating UI with screenshots You can attach images to your prompts that the models can understand using computer vision. To the left of the send button, there is a little button to attach an image from your computer. This functionality is incredibly useful for generating UI code, whether you are giving it an example UI as a reference for generating new UI in your application or providing a screenshot of existing UI in your application and prompting it to change details in reference to the image. Cursor Rules Cursor Rules allow you to add additional information that the LLM models might need to provide the best possible experience in your codebase. You can create global rules as well as project-specific ones. An example use case is if your project has some updated dependency with newer APIs than the one on which the LLM has been trained. I ran into this when adding Tailwind v4 to a project; the models are always generating code based on Tailwind v3 or earlier. Here’s how we can add a rules file to handle this use case: ` If you want to see some more examples, check out the awesome-cursorrules repository. Summary Learn to use Cursor and similar tools to enhance your development process. It may not give you actual superpowers, but it may feel like it. All the features and tools we’ve covered in this post come together to provide an amazing experience for developing all types of software and applications....

Apr 18, 2025

11 mins

AICursor

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Getting Started with React and TypeScript

Getting Started with React and TypeScript

Prerequisites

Create React App

Folder Structure

Hello, World - With TypeScript and React

Adding a bit of TypeScript

Benefits of TypeScript

Conclusion

Matthew Pagan

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