# Warning: Support for defaultProps will be removed from function components in a future major release.

**Code:** `defaultProps deprecated` · **Category:** React · **Seen on:** React

A function component (often inside a library) uses Component.defaultProps.

## Meaning

React 18.3 warns; React 19 removes defaultProps for function components. Use JavaScript default parameters instead.

## Common causes

- Your components using defaultProps
- Old library versions using defaultProps

## Quick fix

1. Use default parameters: function Btn({ size = 'md' })
2. Upgrade libraries

## Detailed fix by platform

### React

1. `function Avatar({ size = 40, alt = '' }) { … }`

## How to diagnose

1. **Source** — Your code or a library?
2. **Recent change** — Did it start after a deploy, upgrade, or configuration change? Compare with the last working version.

---
Source: [WhatIsMyError](https://whatismyerror.com/errors/react/defaultprops-will-be-removed)