Introduction to useEffect

The useEffect hook lets you perform side effects in React components. Side effects are operations that interact with the outside world or need to happen after render.

What are Side Effects?

Side effects are anything that happens outside of React's rendering process:

Why useEffect?

In React, the render function should be pure. Side effects need a special place to run:

How useEffect Works

The effect runs after every render by default:

Basic useEffect Syntax

The hook takes a function that contains your side effect code:

Common Use Case: Document Title

One of the simplest examples of useEffect:

Exercise: Identify Side Effects

Exercise: Simulate Effect Timing

Exercise: Document Title Effect

Key Takeaways

1. Side effects - Operations that interact with the outside world
2. useEffect timing - Runs AFTER render, not during
3. Pure renders - Keep render functions pure, move side effects to useEffect
4. Common uses - Document title, logging, data fetching, subscriptions
5. Effect function - The first argument to useEffect contains your side effect code