Information Flow in React
Tags: react, beginners
Published: 2023-04-06 16:36:38

React is a popular framework used to create web applications because it manages the state of the application, renders components, and has an efficient and effective way of handling information flow. Understanding the importance of information flow between components in React is crucial in developing efficient and maintainable applications.

I just finished a phase in my coding boot camp going over React, and although I'm still far from being an expert, I believe I can offer a good perspective on the importance of information flow in React applications. When I first began my React journey, I always found myself setting state in the first component where I needed it, and forgot to ask myself the question: "What other components might need access to this information?". I quickly found out the importance of information flow when React applications began to become more complex and the challenges that came with managing the flow of information between different components. This entire process became so much easier by simply planning out my component hierarchy prior to building the application.

One of the essential concepts in React is that information can only be shared between a parent and a child component, either passing data down via props or back up via a callback function. This means that if two child components need access to the same information, it's best to have that information stored in a parent component. This is another instance where having a good plan of your component hierarchy and a set end goal for your application can have a dramatic effect on the way you pass information throughout it.

## Passing information as props

I'll start with the easiest way to pass information from one component to another: Parent to Child. This can be achieved via props. Props can be sent from a parent component and accessed in the child component.

In the example below, we have toyData stored in state as toyList in the App component, and we are sending it down to the Toys component via props.

![App - prop](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/m1u23qjafp16df1lxa4w.png)

The Toy component can then access all of the information passed down in toyList and display whatever aspects are wanted to the DOM or even pass the information down as props to another child component.

![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/obxtr6x83iik2n4cwswg.png)

You might be wondering: "Why not just import the toyData directly into the Toys component?". This method would be alright for a very simple react application that doesn't have other components. However, in practical application, keeping toyData available in the App component, allows for easy management of information flow and makes it simple to pass information down to multiple child components that may be created in the future.

## Passing information via callback functions

However, there may be instances where information needs to be passed up from a child component to a parent component. This is where the concept of inverse data flow comes in. This allows a parent component to access data from a child component by utilizing a callback function. Using callback functions is useful when you need to update state in a parent component based on user input in a child component. The parent component would pass down a callback function to the child component via props and then the callback function would be called in the child component, passing some data from the child component into it.

In the example below, a simple NewToy component has been created with an input form to create a New Toy. When the form is submitted, the input values are entered into a key: value pair and saved as a const newToy. 

![NewToy - preAddToy](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/9vhpkaabq2fq6hfsyp7b.png)

We need to get this data back into our parent component, the App component. To achieve this, we create a callback function in our parent component and call it in the child component.

![App - AddToy](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/gaiydzyym6dvh5bzvinv.png)

![NewToy - AddToy](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/ulp4ir9c0js1ie2mtapy.png)

Now, when we run the handleSumbit function, we can pass our addToy function into it as a callback and pass it the newToy const. Then our newToy can be accessed by the App component and update the toyList to reflect the added toy.

In summary, the importance of information flow in React cannot be overstated. It is important to plan the information flow before starting to build the application, especially in complex applications. It's important to pay attention to component hierarchy and think about which components need access to which data. The ability to pass information as props or via callback functions makes it easy to manage information flow efficiently. By understanding these concepts, developers can create applications that run more efficiently and are easier to read and debug when necessary.