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Overview

Functions let you create computed attributes with JavaScript. Use a Function when you need a value that is not already stored on the product, such as discount percentage, SKU coverage, average margin, or a custom label based on several product fields. A Function has three parts:
  • Input query — The product data the Function can read.
  • JS function — The JavaScript that calculates the value.
  • Output schema — The type and shape of the value the Function returns.
Functions run during catalog processing. After a Function is saved and compiled, Layers recalculates products in the background and stores the returned value as a computed attribute.
The JS function editor is currently in beta. Existing derived attributes and legacy computed attributes continue to work.

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Prerequisites

Before you create a Function, make sure:
  • Your products have completed a catalog sync.
  • The product data you want to use exists in Layers, such as variants, tags, prices, metafields, or collection titles.
  • You know how the result should be used: searchable, filterable, sortable, visible in API responses, or available as a storefront facet.

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Create a Function

1

Open Attributes

Go to Catalog & Data > Attributes, then click Create Attribute.
2

Select Computed Attribute

Select Computed Attribute. This opens the Function editor.
3

Name the attribute

Enter a clear name, such as “Discount Percentage” or “Inventory Health”. Layers creates a computed attribute code from the name. Codes start with calculated. and can contain only letters, numbers, underscores, hyphens, and periods. Layers rejects any other characters when you create the attribute.
4

Choose a template or start from scratch

Click Templates to start from a built-in recipe, or write your own Function in the editor.
5

Define the input query

In Select inputs, select only the product fields your Function needs. Smaller input queries are easier to review and faster to process.
6

Define the output schema

In Define outputs, describe the value your Function returns. The schema tells Layers whether the result is a number, string, boolean, array, or object.
7

Preview with a product

Open Test results, select a product, and click Run. Review Received data and Returned data before saving.
8

Save the attribute

Save the attribute. Layers compiles the Function and recalculates product values in the background.

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Input query

The input query controls what product data your Function receives. You can use fields such as:
  • title, vendor, productType, handle
  • available, publishedAt, createdAt, updatedAt
  • tags, namedTags, collectionTitles
  • priceRange
  • variants
  • metafields
  • category, options, images, featuredMedia
For variant data, select the variant fields you need, such as price, compareAtPrice, cost, sku, available, inventoryQuantity, or createdAt.
Use Received data in Test results to confirm the exact data shape before you save.

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Output schema

The output schema tells Layers what your Function returns. Supported output types are:
  • number
  • string
  • boolean
  • array
  • object
For a single returned value, use one output field. Layers stores the value directly on the computed attribute. For multiple returned values, define multiple output fields. Layers stores the parent result as an object and creates generated sub-fields for each output field. You can configure each sub-field for filtering, sorting, and faceting separately.
If a Function returns null, or returns an empty value for a product, Layers excludes that computed value from the product. This keeps empty computed attributes out of API responses and facet results.

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Preview and compile status

The editor shows a compile status:
  • Not compiled — The Function has not been compiled yet.
  • Queued — The Function is waiting to compile.
  • Compiling — Layers is compiling the Function.
  • Ready — The Function compiled successfully and can run during catalog processing.
  • Failed — Layers could not compile the Function. Review the compile error in the editor.
Status updates appear in real time, so you do not need to refresh the page while a Function compiles. Layers also shows the status as a colored dot next to each computed attribute on the Attributes list. Hover the dot to see the current state, or the error message if a compile fails. Use Test results before saving. The preview shows:
  • Console output — Logs captured while the Function ran.
  • Received data — The input assembled from your input query.
  • Returned data — The value returned by the Function.

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Runtime statistics

Once a saved Function starts running during catalog processing, the editor shows a Runtime line under the JavaScript function section. Use it to spot slow or failing Functions without leaving the editor. The line summarizes the current Function version over the last 24 hours, or the last 7 days if there is no recent activity:
  • Runs — How many times the Function executed.
  • Call p95 — The 95th percentile execution time of your JavaScript.
  • Avg total — The average end-to-end time per run, including input preparation and output handling.
  • Build — The average time spent preparing the compiled Function before it runs.
  • Timeouts and failures — Shown in red when any runs timed out or failed.
  • Retries — Shown when any runs were retried.
Statistics are tracked per Function version. When you save a change that republishes the Function, the new version starts with fresh statistics, so timings from old source code never mix with the new version. The Runtime line is hidden when the Function has no recorded runs in the last 7 days, such as a newly created Function that has not processed products yet. New runs appear in the statistics within a few minutes.

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Function limits

Functions are designed for product data transformation. They must be synchronous and self-contained. Supported:
  • Plain JavaScript helper functions.
  • Array methods such as map, filter, and reduce.
  • Built-in JavaScript methods for strings, numbers, objects, arrays, dates, Math, and JSON.
Not supported:
  • Imports or require.
  • Network calls such as fetch.
  • Async functions, await, and Promise APIs.
  • Timers such as setTimeout or setInterval.
  • Classes.
  • for, for...of, for...in, while, and do...while loops.
  • Recursive functions.

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Troubleshooting

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The Run button is disabled

Select a product in the Preview panel and make sure the editor does not show a blocking syntax error.

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The Function returns no value

Check Received data to confirm your input query includes the field you expect. If the input is empty, add the missing field to the input query.

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A returned field is missing

Compare Returned data with your output schema. Required fields must be returned for every product where the Function produces a result.

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The output type is rejected

Make sure the returned value matches the output schema. For example, a boolean field must return true or false, not "true" or "false".

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The Function compiles but products do not show values yet

Product recalculation runs in the background after you save. Check again after processing finishes, and confirm the attribute is configured for the place you expect to use it, such as API visibility, filtering, sorting, or storefront facets.

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Next steps