Most Annoying Errors in React and How to Fix Them

on

 React is a powerful frontend library, but it comes with its share of frustrating errors that can leave developers scratching their heads. In this post, we’ll discuss some of the most annoying React errors and how to fix them quickly.

 


1. Too Many Re-renders (Infinite Loop) 🌀

Error:

plaintext 
Error: Too many re-renders. React limits the number of renders to prevent an infinite loop.

Cause:

This happens when state updates continuously trigger component re-renders, leading to an infinite loop.
🔹 Example:

jsx 
const [count, setCount] = useState(0);

setCount(count + 1); // Updates state on every render

Fix:

Always update state inside an event handler or useEffect:

const [count, setCount] = useState(0);

useEffect(() => {
  setCount(prev => prev + 1);
}, []); // Only runs once

2. Objects Not Being Tracked in State 🔄

Error:

Your component does not update even when an object in the state changes.
🔹 Example:

jsx 
const [user, setUser] = useState({ name: "Aryan" });

user.name = "Aditi"; // React does not track this change

Fix:

Always use setState with a new object reference:

jsx
setUser(prev => ({ ...prev, name: "Aditi" }));

3. Cannot read properties of undefined 📛

Error:

plaintext 
TypeError: Cannot read properties of undefined (reading 'map')

Cause:

Trying to .map() over undefined or null.
🔹 Example:

jsx 
const [items, setItems] = useState();

return 
    {items.map(item => 
  • {item}
    • )}
; // Error!

Fix:

Always initialize state with an empty array:

jsx 
const [items, setItems] = useState([]);

4. render is not a function ❌

Error:

plaintext 
TypeError: render is not a function

Cause:

Calling .render() on an incorrect type (e.g., calling a function on an object).
🔹 Example:

jsx
const Component = { render: () => <h1>Hello </h1> };

return <component> ;// Error!
</component>

Fix:

Ensure Component is a function or class: 

jsx 
const Component = () =>   <h1>Hello </h1> };

return <component>;
</component>

5. Expected an assignment or function call but saw an expression ⚠️

Error:

plaintext 
Expected an assignment or function call and instead saw an expression.

Cause:

Using an arrow function without returning JSX.

🔹 Example: 

jsx
const Button = () => (console.log("Clicked")); // Does not return JSX

Fix:

Wrap the function in {} and return JSX:

jsx 
const Button = () => {
  console.log("Clicked");
  return %gt;button<Click Me%gt;/button<;
};

6. React Hook useEffect has a missing dependency ⚡

Error:

plaintext 
React Hook useEffect has a missing dependency: 'someValue'. Either include it or remove the dependency array.

Cause:

useEffect depends on a variable but doesn't include it in the dependency array.

Example:

jsx 
useEffect(() => {
  console.log(someValue);
}, []); // someValue is missing
 

Fix:

Include someValue in the dependencies: 

jsx 
useEffect(() => {
  console.log(someValue);
}, [someValue]);

7. Can't perform a React state update on an unmounted component 🛑

Error:

plaintext 
Warning: Can't perform a React state update on an unmounted component.

Cause:

Updating state after a component unmounts (e.g., inside an async function).

🔹 Example: 

jsx 
useEffect(() => {
  fetchData().then(data => setItems(data)); // Might update after unmount
}, []);
 

Fix:

Use useRef to track if the component is mounted: 

jsx 
const isMounted = useRef(true);

useEffect(() => {
  return () => (isMounted.current = false);
}, []);

useEffect(() => {
  fetchData().then(data => {
    if (isMounted.current) setItems(data);
  });
}, []);

Conclusion

React errors can be frustrating, but most of them have simple fixes once you understand their root causes. Always ensure:
✔️ Your components are properly structured.
✔️ State updates follow best practices.
✔️ Hooks are used correctly.

Did you face any other React errors? Comment below, and let’s debug them together! 🚀

 

Keywords:

React common errors, React debugging, JavaScript errors in React, React troubleshooting, Fix React infinite loop, React useEffect errors, React hook issues, Best practices in React.