# How to call Functions from iOS Twilio Functions are a perfect fit for mobile app developers. You can focus on writing your app, and let Twilio host and run the server code you need. You don't need a special SDK to call Twilio Functions from your mobile app—your Function will respond to a normal HTTP call, making it accessible from standard iOS Networking code. In this guide, we'll show you how to set up a Twilio Function, call it from a web browser, and then call that function from an iOS application. Our Function will return a joke as a string. You could extend it to make it choose a random joke from a list, or by category. We'll keep it brief, and just return a hard coded string. Let's start by creating a Function and giving it the path of `/joke`. Be sure to set the visibility of this Function to **public**, to avoid any hurdles when making your HTTP calls: ## Create and host a Function Before you run any of the examples on this page, create a Function and paste the example code into it. You can create a Function in the Twilio Console or by using the [Serverless Toolkit](/docs/labs/serverless-toolkit). ## Console If you prefer a UI-driven approach, complete these steps in the Twilio Console: 1. Log in to the [Twilio Console](https://1console.twilio.com) and navigate to **Develop > Functions & Assets**. If you're using the *legacy* Console, open the [**Functions** tab](https://www.twilio.com/console/functions/overview). 2. Functions are contained within **Services**. Click **[Create Service](https://www.twilio.com/console/functions/overview/services)** to create a new **[Service](/docs/serverless/functions-assets/functions/create-service)**. 3. Click **Add +** and select **Add Function** from the dropdown. 4. The Console creates a new [protected](/docs/serverless/functions-assets/visibility) Function that you can rename. The filename becomes the URL path of the Function. 5. Copy one of the example code snippets from this page and paste the code into your newly created Function. You can switch examples by using the dropdown menu in the code rail. 6. Click **Save**. 7. Click **Deploy All** to build and deploy the Function. After deployment, you can access your Function at `https://--.twil.io/`\ For example: `test-function-3548.twil.io/hello-world`. ## Serverless Toolkit The [Serverless Toolkit](/docs/labs/serverless-toolkit) lets you develop locally, deploy projects, and perform other tasks through the [Twilio CLI](/docs/twilio-cli/quickstart). 1. From the CLI, run `twilio serverless:init --empty` to bootstrap your local environment. 2. Go to your new project directory using `cd `. 3. In the `/functions` directory, create a JavaScript file whose name reflects the purpose of the Function. For example, `sms-reply.protected.js` for a [protected](/docs/serverless/functions-assets/visibility) Function intended to handle incoming SMS. 4. Add the code example of your choice to the file and save it. Note that a Function can only export a single handler. You need to create separate files to run or deploy multiple examples at once. After you save the Function code, you can test it locally (and optionally tunnel requests to it using a tool like [ngrok](https://ngrok.com/)), or deploy it. ### Run your Function in local development Run `twilio serverless:start` from your CLI to start the project locally. The Function(s) in your project are accessible from `http://localhost:3000/sms-reply` * If you want to test a Function as a [Twilio webhook](/docs/usage/webhooks/getting-started-twilio-webhooks), run: `twilio phone-numbers:update --sms-url "http://localhost:3000/sms-reply"`\ This automatically generates an ngrok tunnel from Twilio to your locally running Function, so you can start sending texts to it. You can apply the same process but with the `voice-url` flag instead to test with [Twilio Voice](/docs/voice). * If your code does *not* connect to Twilio Voice or Messages as a webhook, start your dev server and start an ngrok tunnel in the same command with the `ngrok` flag. For example: `twilio serverless:start --ngrok=""` ### Deploy your Function To deploy your Function and have access to live url(s), run `twilio serverless:deploy` from your CLI. This deploys your Function(s) to Twilio under a development Environment by default, where they can be accessed from: `https://--dev.twil.io/` For example: `https://incoming-sms-examples-3421-dev.twil.io/sms-reply` You can now invoke your Function with HTTP requests, configure it as the [webhook](/docs/usage/webhooks/getting-started-twilio-webhooks) for a Twilio phone number, call it from a Twilio Studio [**Run Function** Widget](/docs/studio/widget-library/run-function), and more. With the Function created, we'll need to edit the boilerplate code that is generated for the Function—by default, it comes with some code to return TwiML. We're only going to return a joke. And it's a bad joke. ```js title="Return a Joke with a Twilio Function" exports.handler = (context, event, callback) => { const joke = 'How many apples grow on a tree? They all do!'; return callback(null, joke); }; ``` Copy the above code into the Twilio Functions code editor. Please, change the joke to something better. Press the **Save** button to save that code, and **Deploy All** to deploy your Function. ## Call a Twilio Function from the Web To call your new Function from the web, get the Function's URL by clicking the Copy URL icon next to the path, and then paste that URL into any web browser (you don't have to be authenticated with Twilio). You'll get a text response containing whatever you return from your Function! ## Call a Twilio Function from iOS We can use the standard iOS library to call our Twilio Function. The `URLSession` (`NSURLSession` with Objective-C) class lets us create a data task that takes a URL and a closure (completion block in Objective-C) as an argument. Your closure will get the HTTP response, the `Data`/`NSData` returned by the server, and an error (if there was one) as arguments. We check to see if the error exists, and if it does not, we create a string from the `Data` and print it out. Be sure to call resume on the task to initiate the HTTP Request—this step is commonly forgotten. Call a Twilio Function from iOS ```objective-c NSString* functionURL = @"https://yourdomain.twil.io/joke"; NSURL *url = [NSURL URLWithString:functionURL]; NSURLSessionDataTask *task = [[NSURLSession sharedSession] dataTaskWithURL:url completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) { if (error) { NSLog(@"Error: %@",error); } else { NSString *responseString = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding]; NSLog(@"Response: %@", responseString); } }]; [task resume]; ``` ```swift let functionURL = "https://yourdomain.twil.io/joke" if let url = URL(string: functionURL) { let task = URLSession.shared.dataTask(with: url) { data, response, error in if error != nil { print(error!) } else { if let responseString = String(data: data!, encoding: .utf8) { print(responseString) } } } task.resume() } ``` > \[!WARNING] > > If you are calling Twilio Functions from an Xcode Playground with Swift, you will need to tell the Playground to run indefinitely (so the HTTP call can return). > > To do this, you will need to import the `PlaygroundSupport` framework, and then include this line of code at the bottom: > > `PlaygroundPage.current.needsIndefiniteExecution = true` ## Return JSON from a Twilio Function Our previous example Function returned plain text. You can also return JSON from a Twilio Function, by passing a JavaScript object or array to the `callback` function. For instance, we can create another Twilio Function to return a list of jokes, along with an id and a favorite count. Create a new Function with a path of `/jokes`. ```js title="A Twilio Function that Returns a JSON Array" exports.handler = (context, event, callback) => { const knockKnock = { id: 1, text: 'Knock, knock', favorited: 37 }; const chicken = { id: 2, text: 'Why did the chicken cross the road?', favorited: 12, }; const jokes = [knockKnock, chicken]; return callback(null, jokes); }; ``` ## Parse JSON from a Twilio Function From iOS, we call this Function the same way that we did our first Function (don't forget to change the path to `/jokes`). Instead of creating a `String`/`NSString` from data, we will use iOS's built-in JSON Serialization to parse the response data into an array. Call a Twilio Function that returns JSON from iOS ```objective-c NSString* functionURL = @"https://yourdomain.twil.io/jokes"; NSURL *url = [NSURL URLWithString:functionURL]; NSURLSessionDataTask *task = [[NSURLSession sharedSession] dataTaskWithURL:url completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) { if (error) { NSLog(@"Error: %@",error); } else { NSError *error; id responseObject = [NSJSONSerialization JSONObjectWithData:data options:0 error:&error]; NSLog(@"Response: %@", responseObject); } }]; [task resume]; ``` ```swift let functionURL = "https://yourdomain.twil.io/jokes" if let url = URL(string: functionURL) { let task = URLSession.shared.dataTask(with: url) { data, response, error in if error != nil { print(error!) } else { do { let responseObject = try JSONSerialization.jsonObject(with: data!) as! [[String:Any]] print(responseObject) } catch let error as NSError { print(error) } } } task.resume() } ``` You've now seen how to run Node.js code as a Twilio Function, and how your mobile application can use this as a serverless backend to provide data for your application. Where to go next? You could extend the Function to choose a random joke from that array. You can also use Twilio functionality from inside your Function, for instance to send an SMS, or to return an access token for Video, Chat, or Sync. Check out the [Programmable SMS Quickstart for Twilio Functions](/docs/serverless/functions-assets/quickstart/receive-sms) and [Programmable Voice Quickstart for Twilio Functions](/docs/serverless/functions-assets/quickstart/receive-call) for more quick introductions to these key features of Functions.