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Serverless Functions for React Native: The Power of Expo and AWS Lambda

Published June 30, 2025
Updated June 30, 2025
5 min read

Learn how to seamlessly connect your React Native mobile app with a powerful serverless backend using Expo and AWS Lambda. This post explores the benefits, practical steps, and a simple example to get you started with this modern architecture.

In today’s fast-paced mobile development world, building a robust and scalable backend for your React Native app can often feel like a daunting task. You have to manage servers, handle scaling, and worry about security—all while trying to deliver a great user experience. But what if you could have a powerful, scalable backend without any of that overhead? That’s where serverless architecture comes in.

This post will show you how to connect your React Native app, specifically with Expo, to a serverless backend using AWS Lambda. By the end, you’ll understand why this combination is a game-changer and how to get started.

Why Serverless for Mobile Apps? 💡

Serverless architecture, particularly with services like AWS Lambda, allows you to run code without provisioning or managing servers. You simply upload your function, and the cloud provider handles everything else. For a React Native app, this offers several compelling advantages:

  • Cost-Efficiency: You only pay for the compute time you consume. If your app has low usage, your costs are minimal. This is a huge win compared to paying for a server that’s idle most of the time. 💸
  • Automatic Scaling: Your functions scale automatically to handle thousands of requests per second. Whether you have 10 users or 10 million, your backend can handle the load without you needing to manually adjust anything. 🚀
  • Simplified Development: You can focus on writing the business logic for your backend without getting bogged down in server management, operating system updates, or security patches. This accelerates your development cycle.
  • Reduced Latency: You can deploy your functions in multiple regions worldwide, allowing you to serve your users from the closest possible location, which reduces latency and improves app performance.

The Expo and AWS Lambda Combo 🤝

Expo is a fantastic framework for building universal React Native apps. It provides a managed workflow that simplifies the build process, handles native modules, and offers a vast ecosystem of pre-built components. When you combine this with AWS Lambda, you create an incredibly powerful and efficient development stack.

Expo’s fetch API, a standard part of the web platform, makes it incredibly easy to call any API endpoint. This means you can simply make a standard HTTP request from your React Native app to an AWS Lambda function, which is exposed via an API Gateway endpoint.

“The beauty of this architecture lies in its simplicity. Your mobile app becomes a lean client that consumes services, and your backend logic is encapsulated in small, purpose-built functions. This separation of concerns leads to a more maintainable and scalable codebase.”

Practical Example: A Simple Todo List App 🛠️

Let’s walk through a simple use case: building a serverless backend for a React Native todo list app. Our goal is to create a function that handles adding new todo items to a database, like Amazon DynamoDB.

Step 1: Set up Your AWS Lambda Function

First, you’ll need an AWS account. Once you’re in the AWS console, navigate to the Lambda service.

  1. Create a Function: Click “Create function” and choose a meaningful name, like createTodoItem. Select Node.js as the runtime, as it’s a perfect fit for this kind of work and plays well with the JavaScript ecosystem.
  2. Write Your Code: The core of your function is just a simple JavaScript file. Your function will receive an event object, which contains data from the API Gateway, including the todo item’s text.
// index.js for AWS Lambda
const AWS = require('aws-sdk');
const docClient = new AWS.DynamoDB.DocumentClient();

exports.handler = async (event) => {
    const todoItem = JSON.parse(event.body);
    const params = {
        TableName: 'Todos',
        Item: {
            'todoId': Date.now().toString(),
            'text': todoItem.text,
            'completed': false
        }
    };

    try {
        await docClient.put(params).promise();
        return {
            statusCode: 200,
            body: JSON.stringify({ message: "Todo item created successfully!" })
        };
    } catch (err) {
        console.error(err);
        return {
            statusCode: 500,
            body: JSON.stringify({ message: "Failed to create todo item." })
        };
    }
};
  1. Configure an API Gateway Trigger: To make your function accessible from your React Native app, you need to add an API Gateway trigger. This will give you a public URL that your app can call. Make sure to enable CORS (Cross-Origin Resource Sharing) to allow requests from your app.

Step 2: Call the Lambda Function from Your Expo App

Now, in your Expo-based React Native app, you can use the standard fetch API to call the API Gateway URL.

// App.js in your Expo project
import React, { useState } from 'react';
import { View, Button, TextInput, StyleSheet, Alert } from 'react-native';

const API_ENDPOINT = "YOUR_API_GATEWAY_URL"; // Replace with your URL

export default function App() {
    const [todoText, setTodoText] = useState('');

    const createTodo = async () => {
        try {
            const response = await fetch(API_ENDPOINT, {
                method: 'POST',
                headers: {
                    'Content-Type': 'application/json',
                },
                body: JSON.stringify({ text: todoText }),
            });

            if (response.ok) {
                Alert.alert("Success", "Todo item created!");
                setTodoText('');
            } else {
                Alert.alert("Error", "Failed to create todo item.");
            }
        } catch (error) {
            console.error(error);
            Alert.alert("Error", "Network request failed.");
        }
    };

    return (
        <View style={styles.container}>
            <TextInput
                style={styles.input}
                value={todoText}
                onChangeText={setTodoText}
                placeholder="Enter a new todo item"
            />
            <Button title="Add Todo" onPress={createTodo} />
        </View>
    );
}

const styles = StyleSheet.create({
    container: { flex: 1, justifyContent: 'center', padding: 20 },
    input: { height: 40, borderColor: 'gray', borderWidth: 1, marginBottom: 10, padding: 8 }
});

This simple example demonstrates the seamless connection. Your React Native app sends a JSON payload, the API Gateway routes it to your Lambda function, which processes the data and sends a response back. All without you ever needing to worry about a server.

The Future is Serverless 🌟

Connecting your React Native app to a serverless backend with Expo and AWS Lambda is not just a trend; it’s a modern, efficient, and cost-effective way to build applications. It frees you from the complexities of server management, allowing you to focus on what you do best: building amazing mobile experiences.

By leveraging these powerful tools, you can build scalable, high-performance applications faster than ever before. So, next time you start a new React Native project, consider going serverless. Your future self (and your wallet) will thank you. 🤝