Custom Code

The Custom Code tool allows you to add complex logic to a workflow that might otherwise be difficult with MESA’s built-in tools. You can create custom integrations to third-party services, even those that MESA does not yet integrate, and code custom business logic using JavaScript.

Configure

To open the code editor

Click the </> Edit Code button to edit your custom code.

Anatomy of a Custom Code step

const Mesa = require('vendor/Mesa.js');

/**
 * A MESA Script exports a class with a script() method.
 */
module.exports = new class {

  /**
   * MESA Script
   *
   * @param {object} prevResponse The response from the previous step
   * @param {object} context Additional context about this task
   */
  script = (prevResponse, context) => {

    // Retrieve the Variables Available to this step
    const vars = context.steps;

    // Add your custom code here
    let response = {}

    // Call the next step in this workflow
    // response will be the Variables Available from this step
    Mesa.output.next(response);
  }

}

Code is executed in a V8 environment and can be written in standard JavaScript or ES6. When this step is run, the script() method will be called with two parameters: prevResponse and context. In order for your workflow to continue its subsequent steps, be sure to include a call to Mesa.output.next(response); somewhere within your script() method.

Thecontext object

Property	Type	Description
steps	Object	An object containing the variables for each step that has been run so far, named with the step's unique key. For example, to access a step with a key of "shopify" use: context.steps['shopify'].
trigger	Trigger	This object is the configuration of the current step being run.
task	Task	This object is information about the current task's execution.

TheTrigger object

Property	Type	Description
metadata	Object	The values entered in configuration fields, with variable replacements.
raw_metadata	Object	The values entered in configuration fields, without variable replacements.
fields	Object	An object of the configuration fields from the UI.

TheTask object

Property	Type	Description
context.headers	Object	A key-value object of the HTTP headers passed to this task.
is_test	Object	Is the current task being run as a test?

Using Libraries

Libraries offer built-in functionality that extends the power of your code. The MESA SDK library is included by default and other libraries can be imported as needed.

Going Further

Logging information

To debug your script, it can be helpful to log data at a particular step in your code. This can be done by calling Mesa.log.info(). This is equivalent to console.log() in browser-based JavaScript. When the workflow runs, the info will be available in your workflow’s Logs tab.

Throwing errors

Throw a JavaScript error to halt the execution of your workflow:

throw new Error("your error description")

In the User Interface, this will look like:

Interacting with external APIs

Use Mesa.request.get() to make HTTP requests to external APIs. This is the equivalent to fetch() in browser-based JavaScript.

Technical Notes

Timezones

All system timezones use your Shopify Store’s timezone. You can view and update your timezone from the Shopify Dashboard: Admin > Settings > General, under “Standards and formats”. If you need to get dates in a different timezone, use the Mesa.date.setTimezone(timezone) method.

Unsupported NodeJS methods

Scripts are run in a stock V8 environment. This means that some common NodeJS methods are not available:

• request(): Alternative: Mesa.request.*() Documentation.
• console.log(): Alternative: Mesa.log.*() Documentation.
• async or await: All Mesa.request.*() methods are synchronous, so async and await are not necessary.
• DOM manipulation methods: Alternative: Mesa.xml.decode() Documentation.

In this section

LibrariesReference index of the JavaScript libraries available in MESA custom code, including the SDK, Shopify, ShopifyGraphql, Oauth, Filter, Loop and Transform.

FAQAnswers to common MESA custom code questions, including why fetch is unavailable in the V8 environment, how to use MESA.request, and how to throw errors.