Add delay

(error)

Danger

Functions are subject to a 10-second execution limit before being terminated. Keep this limit in mind when evaluating if this method suits your use case.

Adding a delay to your Function's response is useful in certain use cases, particularly when it comes to interacting with Twilio Studio. One such case is if you are creating a chatbot and want longer, more realistic pauses between responses. Or perhaps you are making an HTTP request in a Studio Flow and want to add a delay to the retry loop on failure.

In all of these situations, the ability to add a delay is incredibly helpful. While Studio does not provide a native "Delay" widget, you can combine the Run Function widget with a Function that has a delayed response to emulate such behavior.

Below are some examples of what such a Function may look like. Before getting deeper into the examples, first, create a Service and Function so that you have a place to write and test your Function code.

Create and host a Function

In order to run any of the following examples, you will first need to create a Function into which you can paste the example code. You can create a Function using the Twilio Console or the Serverless Toolkit as explained below:

ConsoleServerless Toolkit

If you prefer a UI-driven approach, creating and deploying a Function can be done entirely using the Twilio Console and the following steps:

Log in to the Twilio Console and navigate to the Functions tab. If you need an account, you can sign up for a free Twilio account here!
Functions are contained within Services. Create a Service by clicking the Create Service button and providing a name such as test-function.
Once you've been redirected to the new Service, click the Add + button and select Add Function from the dropdown.
This will create a new Protected Function for you with the option to rename it. The name of the file will be path it is accessed from.
Copy any one of the example code snippets from this page that you want to experiment with, and paste the code into your newly created Function. You can quickly switch examples by using the dropdown menu of the code rail.
Click Save to save your Function's contents.
Click Deploy All to build and deploy the Function. After a short delay, your Function will be accessible from: https://<service-name>-<random-characters>-<optional-domain-suffix>.twil.io/<function-path>
For example: test-function-3548.twil.io/hello-world.

The Serverless Toolkit enables you with local development, project deployment, and other functionality via the Twilio CLI. To get up and running with these examples using Serverless Toolkit, follow this process:

From the CLI, run twilio serverless:init <your-service-name> --empty to bootstrap your local environment.
Navigate into your new project directory using cd <your-service-name>
In the /functions directory, create a new JavaScript file that is named respective to the purpose of the Function. For example, sms-reply.protected.js for a Protected Function intended to handle incoming SMS.
Populate the file using the code example of your choice and save. Note A Function can only export a single handler. You will want to create separate files if you want to run and/or deploy multiple examples at once.

Once your Function(s) code is written and saved, you can test it either by running it locally (and optionally tunneling requests to it via a tool like ngrok), or by deploying the Function and executing against the deployed url(s).

Run your Function in local development

Run twilio serverless:start from your CLI to start the project locally. The Function(s) in your project will be accessible from http://localhost:3000/sms-reply

If you want to test a Function as a Twilio webhook, run: twilio phone-numbers:update <your Twilio phone number> --sms-url "http://localhost:3000/sms-reply"
This will automatically generate 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 if you want to test with Twilio Voice.
If your code does not connect to Twilio Voice/Messages as a webhook, you can 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 will deploy your Function(s) to Twilio under a development environment by default, where they can be accessed from:

https://<service-name>-<random-characters>-dev.twil.io/<function-path>

For example: https://incoming-sms-examples-3421-dev.twil.io/sms-reply

Your Function is now ready to be invoked by HTTP requests, set as the webhook of a Twilio phone number, invoked by a Twilio Studio Run Function Widget, and more!

Create a Delay Function

The act of delaying a Function's response is mostly just a matter of using a built-in method, such as setTimeout, to delay the act of calling the callback method and signaling that the Function has completed. If this Function were to be called by a Run Function widget, the Studio Flow containing that call would be delayed until this Function returns a response.

It's also quite possible to provide the value for delay, by defining a value (or dynamic variable) under the Function Parameters config for the Run Function Widget that calls this Function.

To provide a more async/await friendly syntax in your Functions, this example demonstrates how to write a sleep helper method that wraps setTimeout in a Promise.

If your Function has no other actions to execute or if you don't see the need for Promises in this case, the next example demonstrates the same functionality, but without the async/await abstraction.

Delayed response Function

1// Helper function for quickly adding await-able "pauses" to JavaScript
2const sleep = (delay) => new Promise((resolve) => setTimeout(resolve, delay));
3
4exports.handler = async (context, event, callback) => {
5  // A custom delay value could be passed to the Function, either via
6  // request parameters or by the Run Function Widget
7  // Default to a 5-second delay
8  const delay = event.delay || 5000;
9  // Pause Function for the specified number of ms
10  await sleep(delay);
11  // Once the delay has passed, return a success message, TwiML, or
12  // any other content to whatever invoked this Function.
13  return callback(null, `Timer up: ${delay}ms`);
14};

Delayed response Function

Without async/await or Promises

1exports.handler = (context, event, callback) => {
2  // A custom delay value could be passed to the Function, either via
3  // request parameters or by the Run Function Widget
4  // Default to a 5-second delay
5  const delay = event.delay || 5000;
6  // Set a timer for the specified number of ms. Once the delay has passed,
7  // return a success message, TwiML, or any other content to whatever
8  // invoked this Function.
9  setTimeout(() => callback(null, `Timer Up: ${delay}ms`), delay);
10};

Refactoring the sleep method

The sleep method that we created for the previous example is also a great example of a method that could be used across a number of Functions in your Service. In Functions, it's best practice to store shared JavaScript methods such as these in Private Functions, and import them into the various Functions that will make use of them.

To see this in action, first create a new Function named utils, and set its privacy level to Private. Paste in the following code, which exports the sleep helper from before.

Private shared utilities Function

An example of a Private Function which hosts shared methods across Functions

1// Helper function for quickly adding await-able "pauses" to JavaScript
2exports.sleep = (delay) => new Promise((resolve) => setTimeout(resolve, delay));

Next, open your existing Delay Function, remove the inline declaration of sleep, and add the highlighted line of code. Save and deploy all changes.

This is a demonstration of using the Runtime.getFunctions helper to import shared code from a private Function, which can help to DRY up your Functions code.

Delayed response Function

A delayed Function that leverages a utility method instead of defining it inline

1exports.handler = async (context, event, callback) => {
2  // You can import shared code from a Private Function
3  // using the Runtime.getFunctions() helper + require
4  const { sleep } = require(Runtime.getFunctions().utils.path);
5  // A custom delay value could be passed to the Function, either via
6  // request parameters or by the Run Function Widget
7  // Default to a 5-second delay
8  const delay = event.delay || 5000;
9  // Pause Function for the specified number of ms
10  await sleep(delay || 5000);
11  // Once the delay has passed, return a success message, TwiML, or
12  // any other content to whatever invoked this Function.
13  return callback(null, `Timer up: ${delay}ms`);
14};