Where do you initialize state in React Component?

Functional Components are super cool. Though, Classical components are still used & so is the conventional state in those.

State initialization is a very common scenario while developing the components.

But where do you initialize your components’ state?

Let’s looks at the places where it could be initialized.

The obvious constructor

One obvious place to initialize is the constructor of the component. Similar to the following:

class Contacts extends React.Component {
  // ...
  constructor(props) {
    super(props)
    this.state = {
      isLoading: false,
      contacts: [],
      errors: []
    }
  }
  // ...
}

Pros:

Very visible and verbose
Can access props to determine the new state

Cons:

Unnecessary use of super and constructor
Can use props but most of the time it is not needed

The Class property way

class Contacts extends React.Component {
  // ...
  state = {
    isLoading: false,
    contacts: [],
    errors: []
  }
  // ...
}

Pros:

Follows the OOP style of the property declaration
Verbose

Cons:

Can’t use props for initialisation
Less readable for to those who prefer old-style JS

Arguments

Consistency

If you are using one style, you should follow the same style everywhere. As the software will always be evolving, consistency should not block you from writing better code.

Readability

Expecting some pieces of code to be there. Is state is there, I would expect it to be in the constructor or at the beginning of the component. Readability is subjective and prone to habitual needs.

Tools

Modern dev toolchain in Front End will allow you to write small and readable code. And with transpiling (transform + compile), it will be usable for all Browsers.

Using tools at disposal will bring more creative ways to solve problems.

Legacy Code

If the code is Legacy and is stopping you to write better code, it’s time to. Refactor.

ReactJS Specific Reasons

Start thinking about Functional Components and Hooks

const Header = props => (
<header>
  <h1>Title</h1>
  <strong>SubTitle</strong>
</header>
)

Keep the state minimal, try to move the state to parent and use a prop to pass it down
Stateless components are Better as they are better testable ```jsx const Button = props => { const [disabled, setDisabled] = useState(false) return ( <button
```
 disabled={disabled}
 onClick={() => setDisabled(prev => !prev)}
```
>
```
 {props.text}
```
) }

// can become const Button = props => ( <button disabled={props.disabled} onClick={props.setDisabled}

{props.text} ) ```

Compose Components from Props ```jsx const Button = props => ( <button disabled={props.disabled} onClick={props.setDisabled}

{props.spinner}{props.text} )

// can become // children will hold spinner // & parent can decide when to show/hide spinner const Button = props => ( <button disabled={props.disabled} onClick={props.setDisabled}

{props.children} ) const App = () => { const [loading] = false return {loading && } Click me }

* Use DefaultProps in case of Class components
* Use prop destructuring along with Default Values for Functional components
```jsx
const Button = ({
  disabled = false,
  setDisabled = () => {},
  children = null
}) => {
  if (!children) {
    // Dont render without any Button content
    return null 
  }
  return (
    <button
      disabled={disabled}
      onClick={setDisabled}
{children}</button>
  )
}

Conclusion

A small thing to ask where to initialise the state. But in a large codebase, these decisions will improve your daily code efficiency.

What style do you prefer?

Let me know through comments 💬 or on Twitter at @patel_pankaj_ and/or @time2hack

Pankaj Patel

Pankaj Patel

Where do you initialize state in React Component?

The obvious constructor

Pros:

Cons:

The Class property way

Pros:

Cons:

Arguments

Consistency

Readability

Tools

Legacy Code

ReactJS Specific Reasons

Conclusion

Credits