A Deep Dive into componentDidMount and useEffect in React
Tags: react, javascript, webdev, beginners
Published: 2023-08-21 08:35:20

#Introduction
It's been a long time since last post, I have many new posts ready in draft, but let's start with one simple posts which I hope clarify a lot.
As a React developer, you may have come across the terms `componentDidMount` and `useEffect` when working with lifecycle methods and hooks, I mean it is almost impossible to make a React application and not encounter one of those two. Although they both serve similar purposes, they are not interchangeable and have some key differences. In this blog post, we'll take a closer look at each method and when to use them in your React projects.

# componentDidMount
`componentDidMount` is a lifecycle method that is called after a component has been rendered to the DOM. It's commonly used to perform any setup or initialization tasks that need to happen after the component has been rendered. For example, you might use componentDidMount to fetch data from an API, set up a subscription, or add event listeners.


```javascript
class ExampleComponent extends React.Component {
  componentDidMount() {
    // perform setup tasks here
  }

  render() {
    // component render logic here
  }
}
```
One of the key benefits of using componentDidMount is that it guarantees that the component has been rendered before the code inside the method is executed. This can be useful if you need to access the DOM or if you want to be sure that the component is fully rendered before you perform any logic.
**componentDidMount is used in Class components**

#useEffect
`useEffect` is a hook that allows you to synchronize a component with an external system. It's similar to componentDidMount, componentDidUpdate, and componentWillUnmount combined. It allows you to add logic that is executed after the component is rendered, and also allows you to clean up that logic when the component is unmounted.


```javascript
function ExampleComponent() {
  useEffect(() => {
    // perform setup tasks here
    return () => {
      // clean up tasks here
    }
  }, []);

  // component render logic here
}
```
The first argument passed to useEffect is a function containing the logic to be executed after the component is rendered. The second argument is an array of dependencies, which are values that the effect depends on. If any of the dependencies change, the effect will be re-executed.

One of the key benefits of using useEffect is that it allows you to synchronize a component with external systems in a more declarative and efficient way than using lifecycle methods. This can make your code easier to understand, test and reuse.

**useEffect hook is equivalent of componentDidMount in functional components**

#When to use which
As a general rule of thumb, if you're working with class components and you need to perform setup or cleanup tasks that are related to the component's lifecycle, you should use `componentDidMount`. If you're working with functional components and you need to synchronize the component with an external system, you should use `useEffect`.

In practice, you'll often find that you can use either method to accomplish the same task. The key is to understand the trade-offs between the two and choose the one that makes the most sense for your specific use case.

# Conclusion
`componentDidMount` and `useEffect` are both powerful tools that can help you manage the lifecycle of your React components. Understanding the differences between them and when to use them will help you write more maintainable, efficient and organized code.
So now you know what is the main difference between these two and how and when to use them. Follow the guidelines and you will reach full potential of your React application.