Are content fields substituted in the JS tab too?

LIGHTWEIGHT TEMPLATES

Yes. [%% field_name %%] is replaced in all three tabs - HTML/JSX, CSS and JS - before the template is delivered to the browser. The editor offers content-field autocompletion in all three as well.

Two things to keep in mind, both because the substitution is purely textual:

// The field holds a bare string: spring-sale
// ✅ quote it - becomes const campaign = "spring-sale";
const campaign = "[%% campaign_id %%]";
// ✅ backticks work too, and let you mix in more text
const label = `Campaign: [%% campaign_id %%]`;
// ❌ unquoted - becomes const campaign = spring-sale;
const campaign = [%% campaign_id %%];
// The field holds a JS literal: ["news", "sports"]
// ✅ no quotes needed - becomes const ids = ["news", "sports"];
const ids = [%% topic_ids %%];
// ✅ or quote and parse - safer when the value may contain quotes
const ids = JSON.parse(`[%% topic_ids %%]`);

• Whether the token needs quotes depends on the field's value. If the field holds a bare string, quote it - otherwise the substituted text is not valid JS: const c = [%% campaign_id %%]; becomes const c = spring-sale;. If the field already holds a valid JS literal - an array, an object, a number, true - the token can stand on its own without quotes. When the value may itself contain quotes, wrap it in backticks and JSON.parse it.

• A field that does not exist becomes an empty string, not an error and not the token itself. A typo in a field name therefore yields "" at runtime, which is easy to mistake for a data problem. Check the spelling against the Content fields list in the editor.

Editor features, including the content-field picker: Lightweight templates editor.

Last updated: September 18, 2026