Generate UUID in React Native

// npx expo install expo-crypto
import * as Crypto from 'expo-crypto';

// Generate a UUID v4 - works on iOS, Android, and Web
const id = Crypto.randomUUID();
console.log(id);
// → "f47ac10b-58cc-4372-a567-0e02b2c3d479"

// expo-crypto also provides randomBytes for custom entropy needs
const bytes = await Crypto.getRandomBytesAsync(16);

// npm install react-native-uuid
import uuid from 'react-native-uuid';

// No polyfill import needed - handles entropy internally
const id = uuid.v4();
console.log(id);
// → "f47ac10b-58cc-4372-a567-0e02b2c3d479"

import 'react-native-get-random-values';
import { v4 as uuidv4 } from 'uuid';

// Branded type for type safety
type ItemId = string & { readonly _brand: 'ItemId' };

function createItemId(): ItemId {
    return uuidv4() as ItemId;
}

interface ListItem {
    id: ItemId;
    title: string;
    completed: boolean;
}

function createItem(title: string): ListItem {
    return { id: createItemId(), title, completed: false };
}

import 'react-native-get-random-values';
import { v4 as uuidv4 } from 'uuid';
import { FlatList, Text, TouchableOpacity } from 'react-native';
import { useState } from 'react';

export default function TodoList() {
    const [todos, setTodos] = useState([]);

    const addTodo = (text) => {
        setTodos(prev => [...prev, { id: uuidv4(), text, done: false }]);
    };

    return (
        <FlatList
            data={todos}
            keyExtractor={item => item.id}  // UUID as stable key
            renderItem={({ item }) => <Text>{item.text}</Text>}
        />
    );
}

import 'react-native-get-random-values';
import { v4 as uuidv4 } from 'uuid';
import AsyncStorage from '@react-native-async-storage/async-storage';

const DEVICE_ID_KEY = '@device_id';

async function getDeviceId() {
    let id = await AsyncStorage.getItem(DEVICE_ID_KEY);
    if (!id) {
        id = uuidv4();
        await AsyncStorage.setItem(DEVICE_ID_KEY, id);
    }
    return id;
}

import 'react-native-get-random-values';
import { v4 as uuidv4 } from 'uuid';

async function addComment(postId, text, setComments) {
    const tempId = uuidv4();
    const optimisticComment = { id: tempId, text, status: 'pending' };

    // Immediately show in UI
    setComments(prev => [...prev, optimisticComment]);

    try {
        const response = await fetch(`/api/posts/${postId}/comments`, {
            method: 'POST',
            headers: { 'Idempotency-Key': tempId },
            body: JSON.stringify({ text }),
        });
        const saved = await response.json();
        // Replace temp with server-confirmed comment
        setComments(prev => prev.map(c => c.id === tempId ? saved : c));
    } catch {
        // Remove on failure
        setComments(prev => prev.filter(c => c.id !== tempId));
    }
}