Execute JavaScript in Power Automate

You can run JavaScript code directly within a CustomJS action in your Microsoft Power Automate flow. Perfect for data transformations, API calls, and custom business logic.

Quick Start Guide

Step 1: Get Your API Key

1. Visit customjs.space and click Sign in
2. Complete registration by either providing your email and password or using your Google account
3. Once registered, you will be redirected to the CustomJS app dashboard
4. Click Show under API Key to reveal your API key
5. Copy your API key for the next step

Step 2: Create Connection in Power Automate

1. Open your Power Automate flow
2. Add a new action and search for "CustomJS"
3. Select "Inline JavaScript" action
4. When prompted, create a new connection:
   • Connection Name: CustomJS (or any name you prefer)
   • API Key: Paste your API key from Step 1
5. Click Create

Step 3: Find the Inline JavaScript Module

1. In your Power Automate flow, click + New step
2. Search for "CustomJS"
3. Select the "Inline JavaScript" action from the list

Step 4: Write Your JavaScript Code

1. In the Input field, provide data as JSON or plain text
2. In the JavaScript Code field, write your code
3. Make sure to end with a return statement
4. The action returns the result to use in subsequent steps

Video Tutorial

Watch this step-by-step video guide on how to execute JavaScript in Power Automate:

How it works

The customJS action consists of four fields: Connection, Input, JavaScript code and Return Type.

Input variables

Inputs are accessed through the input object. For complex scenarios, you can:

• Pass JSON objects as input (must be valid JSON strings).
• Convert Power Automate arrays to JSON format if needed.

Inputs passed to your script are accessible as an input object. If you're passing multiple variables, it’s recommended to structure them as a JSON object for clarity and ease of use.

Await async results before returning

When using asynchronous code (like fetch, database calls, or API requests), await the result and then return it. If you forget await or don’t return the resolved value, Power Automate will just get a pending Promise, not usable data.

// Incorrect: returns a Promise, not data
return fetch(input.url).then(res => res.json());

// Correct: resolve the Promise before returning
const response = await fetch(input.url);
const data = await response.json();
return {
statusCode: response.status,
data: data
};

Remove inline comments

Inline comments usually work if you place them correctly with line breaks. However, misplaced comments can prevent the code from running as expected. Consider removing them if you have issues.

// return full name
return input.firstName + " " + input.lastName;

return input.firstName + " " + input.lastName;