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React Props and State Explained

What's the difference between these two ways of dealing with data? And how can you put them to good use? Let's clarify things one by one.
Daniel Zacharias

Code Power Team

August 29, 2023

Libraries make the life of a web developer easier. These collections of useful components exist to streamline the process of creating a website or an app. With some knowledge of JavaScript fundamentals and component-based architecture, a framework like React should be very useful to you.

However, there’s one common source of confusion that puts most developers in an uncomfortable position. Yes, we’re talking about React props and state. What’s the difference between these two ways of dealing with data? And how can you put them to good use? Let’s clarify things one by one.

What is React?

Some will refer to it as React.js or ReactJS. Either way, we’re talking about an open-source (and free) JavaScript library. It’s a great selection of code you can use to develop single-page, mobile, or server-rendered apps.

React is not just limited to building user interfaces based on components. It can be used for both client-side and server-side rendering, making it a versatile framework for various types of applications.

So what are props?

One of the reasons for its widespread use is the way the framework enables the building of efficient and scalable structures. The developer can utilize its components to separate the user interface into reusable segments. In this case, the components transmit data to each other. More often than not, they do it through props.

In essence, props (short for properties or proprietary purposes) are read-only components. These objects store the value of attributes of a tag and pass data between React components. The flow is unidirectional, following the parent-to-child pattern. It’s not possible to modify parent data by child elements. This makes props akin to HTML attributes.

Props can also handle user interactions. They achieve this by passing callback functions as props. The child component triggers the function, a desired event occurs, and the parent component responds accordingly.

And what exactly is state?

Here, we have a relatively similar type of code. It’s a structure used to contain information about a component. So far, it sounds almost the same. So what makes it unique? What’s the core difference between React props and state? Unlike props, the data contained in the state can change. Said change normally occurs as a response to some user action or a system event.

As a developer, you ought to keep the state as simple as possible. This will enable the React class component to behave and render as intended. You can’t use it with functional components. Also, employ state sparingly as it may slow down your entire website or app. Class components are used with state, while functional components utilize hooks for managing state.

Remember that you can’t modify state directly. Instead, there are two ways to initialize the state, either inside the constructor or directly inside the class.

The similarities between React props and state

As we have already mentioned, confusion among developers stems from their seemingly identical properties. A beginner in JavaScript will more easily see their similarities.

Both React props and state provide details about an item

They exist in the form of a plain JavaScript object

Each tends to contain default values

Both remain strictly read-only while in use

The differences

Despite these similarities, there are also substantial differences between React props and state. Understanding them can improve your development methodology. Here are the main ones that you ought to keep in mind when working with JavaScript:

  1. With props, components receive information from the outside while, with state, they can generate and manage their own data
  2. Props pass data, state manages it
  3. Data carried by props tends to be read-only; a component can’t modify it
  4. State data is private (and thus inaccessible from the outside) but a component can modify it from within
  5. Props use unidirectional data flow while state can go both ways

Taking advantage of their possibilities

Now that we have explained what props and state are, their similarities and differences, it’s time to move on. We need to focus on their practical use. After all, the purpose of all code is to be useful to the developer. So let’s get cracking.

Which to use and when?

These differences between React props and state should already give you an idea of when to employ each. Basically, you should use state when you want to change something within a component. On the other hand, props are best used when you want components to connect and communicate without changing anything.

How to pass props into components?

The main purpose of this action is to make it possible for components to communicate. This process moves from parent to child by declaring HTML tag attributes. You can use syntax such as “this.props.propName;” to access any prop from within the component class. Here “this.props” denotes the type of object while “propName” serves as the key.

How should you update a component’s state?

When discussing React props and state, we should remember that any component will have an initial state. It’s like a static body ready to start moving. The actual power lies in the process of updating the component’s state. This data change then results in something being displayed on the user interface. There are two ways of doing this.

The setState() method. You’ll want to use this one as a response to event handlers, prop changes, or server responses. Once activated, it enqueues all the updates of the component. Next, said component (and its children) get re-rendered, and the update is complete. It’s a great way of preventing excessive re-renders.

The useState() method. This one is able to declare a state in function-based components. It’s a built-in hook that returns an array with the current state value and a function to update it. Neat, isn’t it?

Making it all work for you

In conclusion, understanding the distinction between React props and state is crucial for web developers working with JavaScript. While props enable the transfer of data between components in a unidirectional flow, state allows components to manage and update their own data. By leveraging the strengths of each, developers can harness the full potential of React to create robust web apps.

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