How do you find and fix memory leaks?

A React Native leak is usually a retained reference: a global event subscription that still points at a component, a timer that never clears, or a promise that resolves after unmount and calls setState. The JS heap grows, or native views stay alive after navigation.

import { useEffect, useState } from "react";
import { Keyboard } from "react-native";

export function useKeyboardHeight() {
  const [height, setHeight] = useState(0);

  useEffect(() => {
    const show = Keyboard.addListener("keyboardDidShow", (event) => {
      setHeight(event.endCoordinates.height);
    });
    const hide = Keyboard.addListener("keyboardDidHide", () => setHeight(0));

    return () => {
      show.remove();
      hide.remove();
    };
  }, []);

  return height;
}

Common leak sources

• AppState, Keyboard, NetInfo and navigation listeners without cleanup
• setInterval or setTimeout that is never cleared
• Async requests that update state after unmount, unless aborted
• Global stores or event emitters retaining screen callbacks
• Large images or base64 strings kept in state or caches
• WebViews and native views that are not torn down properly

AbortController is the clean fix for in-flight requests. Pass its signal to fetch and abort in the effect cleanup. For subscriptions, return the library's remove function rather than a custom flag that only suppresses the warning.