Image of inline JavaScript code in Power Automate

How to write JavaScript code in a Power Automate Flow

Azure, JavaScript, Power Automate, Power Platform / By


Learn how to build a simple Azure Function that lets you execute inline code in your flows! The possibilities are endless – regular expressions, string operations, recursive functions, math operations, and much more. This post contains two parts; how to create the Azure Function and how to execute and use it in Power Automate.

How to create an Azure Function App

In this part, we look at how to set up an Azure Function that we are going to use as a helper for writing inline JavaScript code in a Power Automate cloud flow. This is a step-by-step guide where we go through the steps in Azure for creating an Azure Function App and the function that allows us to write code in Power Automate.

Step 1: Firstly go to your Azure Portal, https://portal.azure.com/ (the link opens in a new tab). I use my MSDN subscription and the free credits in Azure for test purposes. If you don’t have an MSDN subscription or any subscription at all. You get access to the popular Azure services for free in 12 months here, https://azure.microsoft.com/en-us/free/ (the link opens in a new tab). The next step assumes that you are logged into the Azure Portal.

Step 2: When you are logged in to the portal you can an overview of your recent resources and azure services. For example:

Image of the landing page when logged into Microsoft Azure Portal.

Step 3: To create an Azure Function App click on + Create a new resource as shown in the image below. This will open a pane with services that are available to create, proceed to the next step.

Image of the first step when adding a new resource in Azure Portal.

Step 4: In the Create a resource pane search for “Function App”. This will open the creation page of the Function App directly when hitting enter. Proceed with the steps below the image.

Image of the resource list in Azure Portal.

Step 5: Click the create button to start the creation process. Next up is adding information about the resource, like resource group, location, name, and settings for the app.

Image of the pane for creating a Function App resource.

Step 6: In this step, we add the necessary/required basic information for the Function App, where we add information about the resource, like resource group, location, name, and settings for the app.

When naming resources in Azure I like to follow the naming convention that Microsoft recommends as best practice as can be found below.
https://docs.microsoft.com/en-us/azure/cloud-adoption-framework/ready/azure-best-practices/resource-naming (link opens in a new tab).

The basic configuration in this example is as follows, and the basic information pane is shown with multiple images below.

Subscription: My MSDN subscription

Resource Group: rg-powerautomate-dev-weu-001

Function App Name: PowerAutomateHelper (This must be a unique name)

Publish: Code

Runtime stack: Node.js

Version: 12 LTS

Region: West Europe

Image of how it looks when creating a new resource group during the creation of Function App creation.
Image of how it looks when adding basic information for the Function App.

Step 7: The next step in the creation process is to review the information we added for the Function App and the remaining step is to create it. The step looks as follows in the Review + create step in Azure. This starts the deployment progress, as can be seen in the next step.

Image of the Review and Create during the process of adding a Function App.

Step 8: After clicking the create button the deployment process of the resources starts immediately.

Image of the deployment of the Function App is in progress.

And finishes a short time after. To open the Function App click on Go to resource.

Image of the completed deployment process and how to navigate to the Function App.

After opening the Function App click on the Functions item in the side menu. This is where we are going to add a function that allows us to write code in Power Automate.

Image on how to navigate to Functions within a Function App.

After going to Functions we need to complete some steps to create a new function. These steps are as follows and are shown in the image below:
1. Create a new function by clicking Create. When the configuration pane opens follow the steps in the image below.
2. Choose to Develop in portal since we are going to add a simple code snippet.
3. Choose HTTP trigger since we are going to call this function from Power Automate
4. Give the function a name. For example FlowHelper.
5. Set Authentication level to Function.
6. Then click create and we can add the code in the next step.

Image of the steps to create a new function within a Function App.

When clicking on create in the previous step the function gets created.

Image of status after creating a function within a Function App.

Step 9: When the function is created we can add code by going to Code + Test as shown in the image below.

Image on how to navigate to the code editor in Azure Portal for Function Apps.

This opens the code editor of the function and can be seen in the image below.

Image of the Code + Test view in Azure Portal for Function Apps.

Step 10: In this step, we add the code to allow us to write code in Power Automate. Replace the boilerplate code with the code below and click save. The code creates a new function that takes a body parameter and returns the result. When we write code in Power Automate the Function App will execute the code we pass the function and it will return the result. Make sure to save changes after adding the code.

module.exports = async function (context, req) {
    context.res = {
        body: (new Function(req.body))()
    };
}
Image of the Function App code that allows us to write code in Power Automate.

Step 11: Before we move to Power Automate we need to get the function URL, we need this as we are going to call this function from Power Automate. To get the function URL click on the Get function URL and copy the URL as shown in the images below.

Image of the button to get the function app URL.

After clicking the Get function URL it opens a dialog with the link. Choose Copy to clipboard and save the URL for use in the next part of this post.

Image of the URL for the function app.

Step 12: This completes the steps for creating the Function App. In the next part, we look at how we can write inline JavaScript code in Power Automate.

Building the Power Automate Flow

In the previous part created a Function App, and in this part, we look at how we can use that function to write inline JavaScript code in Power Automate. We proceed with a step-by-step walkthrough here as well. In the example we look at how to can replace special characters in a string using JavaScript code within the flow.

Step 1: The first step is to create a new cloud flow. For this example, we create an Instant cloud flow so that we can trigger it manually. In this example, I have a solution called Power Automate Flow that adds the instant cloud flow to. To create a new flow proceed with the steps in the image below.

Image of how to create a new Instant cloud flow within a solution.

Step 2: After the proceeding steps are completed a dialog opens. In the dialog give the flow a name and choose “Manually trigger a flow” and then create. This takes as to the newly created flow. To save the flow an action must be added to be able to save it. We add this in the next step.

Image of the dialog that opens after creating a new instant cloud flow.

Step 3: Next, we add a string variable that contains special characters that we want to replace with an underscore using code. After the flow trigger > Click add a new action > Search for variable > Select Initialize variable.

Image of how to initialize a variable on Power Automate.

Step 4: After adding the variable, give the variable a name, choose a variable type of string, then add a string with special characters.

Image of the creation of a string variable containing special characters in Power Automate.

Step 4: In this step, we add the action that is going to call the Azure Function that will execute the JavaScript code we are going to add in the next step. Click on add a new action and search for HTTP and choose the HTTP action as shown in the image below.

Image of how to add an HTTP action in Power Automate.

Step 5: In the HTTP action we add the URL that we copied from the Function App and in the Body, we can now write JavaScript code that gets executed by the Azure Function and outputs the result that can be used further in the flow. As we see in the next step.

The code in this example uses regex to find and replace characters that don’t match numbers, lower and upper case letters with an underscore. If it recurs multiple underscores in a row it gets replaced by one underscore. For instance, if the string contains multiple special characters in a row that has been replaced. 

string = "@{variables('stringWithSpecialCharacters')}";
stringReplaced = string.replace(/[^a-zA-Z0-9]/g,'_').replace(/___/g,'_').replace(/__/g,'_');
return stringReplaced;
Image of how to fill out the HTTP action for calling the Azure Function and adding JavaScript code to be executed by the function.

Step 6: To see the result from the HTTP action we can create a compose action that will output the result.

Image of how to add the compose action in Power Automate.

Step 7: In the compose action, add the body from the HTTP action

Image of how to add the HTTP body to the compose action.

Step 8: When testing/running the flow we can see that the string with special characters has been replaced with a string where all special characters are replaced with an underscore.

Image of the flow run using Azure Function and inline JavaScript code to replace special characters in the string within Power Automate.

The Flow run of the HTTP action looks like this:

The result of the HTTP action calling the Azure Function within the Power Automate flow.

Hope you found it valuable and see further use cases this can provide.

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