RN Extra — Cheatsheet Python → JavaScript / React Native

Variabili e tipi

Python	JavaScript
x = 1	const x = 1 o let x = 1
x = "ciao"	const x = "ciao"
x = True	const x = true
x = None	const x = null
type(x)	typeof x

Stringhe

Python	JavaScript
f"Ciao {nome}"	`Ciao ${nome}`
s.upper()	s.toUpperCase()
s.lower()	s.toLowerCase()
s.strip()	s.trim()
len(s)	s.length

Liste / Array

Python	JavaScript
lista[0]	arr[0]
len(lista)	arr.length
lista.append(x)	arr.push(x)
lista.pop()	arr.pop()
x in lista	arr.includes(x)
lista.sort()	arr.sort()

Loop e funzioni

Python	JavaScript
def f(x):	const f = (x) => { }
def f(): return x	const f = () => x
lambda x: x*2	(x) => x * 2
for x in lista:	lista.forEach(x => ...)
[x*2 for x in l]	l.map(x => x * 2)
[x for x in l if x>2]	l.filter(x => x > 2)
if x > 0:	if (x > 0) { }

Oggetti / Dict

Python	JavaScript
d = {"a": 1}	const d = {a: 1}
d["a"]	d.a o d["a"]
d.get("a")	d?.a (optional chaining)
{**d1, **d2}	{...o1, ...o2}
for k, v in d.items():	Object.entries(d).forEach(([k,v]) => ...)

---

React Native — Componenti

import { View, Text, Button, TextInput, Image, FlatList, TouchableOpacity, StyleSheet } from 'react-native';
import { useState, useEffect } from 'react';
import AsyncStorage from '@react-native-async-storage/async-storage';

Componente	Codice
View	<View style={...}>
Text	<Text style={...}>testo</Text>
Button	<Button title="..." onPress={fn} />
TextInput	<TextInput value={x} onChangeText={setX} />
Image	<Image source={{uri: '...'}} style={...} />
FlatList	<FlatList data={d} renderItem={({item})=>...} />
TouchableOpacity	<TouchableOpacity onPress={fn}>...
ScrollView	<ScrollView>...</ScrollView>

Stile

const styles = StyleSheet.create({
    container: {
        flex: 1,
        padding: 20,
        backgroundColor: '#fff',
        justifyContent: 'center',
        alignItems: 'center',
    },
});

Stato e effetti

const [x, setX] = useState(0);           // stato
useEffect(() => { }, []);                 // all'avvio
useEffect(() => { }, [x]);               // quando x cambia

Navigazione (Expo Router)

import { router, useLocalSearchParams, Link } from 'expo-router';

router.push('/path');                     // naviga
router.push({ pathname: '/path', params: {id: 1} });  // con parametri
router.back();                             // indietro
const params = useLocalSearchParams();     // leggi parametri
<Link href="/path">Vai</Link>              // link dichiarativo

Persistenza

await AsyncStorage.setItem('key', JSON.stringify(dati));
const json = await AsyncStorage.getItem('key');
const dati = json ? JSON.parse(json) : [];

API

const res = await fetch('https://api.esempio.com/data');
const data = await res.json();

const res = await fetch(url, {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({ titolo: '...' }),
});