Run and debug JavaScript

Execute JavaScript in Flows using inline expressions, evalScript, or runScript with console.log debugging.

This guide explains how to execute JavaScript within your Maestro Flows and how to use logging to debug your scripts.

Execution Methods

Maestro provides three ways to run JavaScript, depending on the complexity of the logic you need to perform.

1. In-line expressions

For simple logic or dynamic values, use the ${} syntax directly inside existing Maestro commands. This is ideal for string concatenation or basic math.

- launchApp
- inputText: ${'User_' + faker.name().firstName()} # Generates a dynamic username
- tapOn: ${maestro.platform === 'ios' ? 'Allow' : 'While using the app'} # Conditional logic

Learn how to generate synthetic data using JavaScript.

2. The evalScript Command

Use evalScript for logic-only steps that do not directly interact with a UI element, such as setting a variable or performing a calculation.

- evalScript: ${output.timestamp = new Date().getTime()} # Store data for later use
- evalScript: ${console.log('Test execution started')} # Inline logging

3. The runScript Command

For complex logic, reusable functions, or long scripts, use runScript to execute an external .js file.

You can pass environment variables to your script using the env attribute, in the same way you pass parameters to subflows. First, use runScript to define the JavaScript file and the variables to be shared with it:

- runScript:
    file: setupUser.js
    env:
       userRole: 'admin' # Pass a parameter to the script

The JavaScript file can then read the environment variable directly to perform necessary actions:

// Access the passed parameter directly by its name
const role = userRole; 
console.log(`Setting up user with role: ${role}`);

Logging and debugging

Maestro supports standard console.log statements to help you debug your scripts and track Flow execution.

When logging with JavaScript in Maestro, keep these points in mind:

• Multiple arguments are not supported: Running console.log('My variable is', variable) will only output My variable is.

• Use template literals or concatenation: To log variables alongside text, use template literals (in external files) or string concatenation.

• Log Destination: Anything output via console.log is captured in the maestro.log file, prefaced with JsConsole.

The following code snippet shows examples of both methods:

console.log('Value: ' + myVar)   // concatenation
console.log(`Value is ${myVar}`) // template literals

Logging with evalScript command

If you want to log something inline, you can use evalScript to output it to the console without creating a separate file.

- evalScript: '${console.log("Value: " + myVar)}'

Don't use template literals in evalScript

Standard JavaScript template literals (using backticks ``` and ${}) will not work inside evalScript because the command itself is already wrapped in a ${...} block.

# Example of incorrect use
- evalScript: console.log(`Value is ${myVar}`)

Use string concatenation instead.

Logging in external files

When using runScript, you can organize your logs within your JavaScript files just as you would in a standard development environment. Here, template literals are fully supported.

The following Flow runs a script which will log a status message:

Flow

- runScript:
    file: script.js

JavaScript file (script.js)

Next steps

Now that you already know how to run and debug JavaScript code in Maestro Flows, access the following guides:

• Manage data and states: Learn how to use the output object.

• Generate synthetic data: Use faker to create dynamic test data.

• Test reports and artifacts: Learn how to access the maestro.log using the --debug-output flag to see your console logs.