Steps

It is possible to define an eager and anonymous module using the importmap declaration, meaning that the module is going to be loaded an executed directly on page load and will not be listed in the importmap.

Step 1

Add the dependency you wish to load eagerly and anonymously.

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <dependencies>
    <!-- ... -->
    <dependency>
      <groupId>my.group.id</groupId>
      <artifactId>my-webjar</artifactId>
      <scope>runtime</scope>
    </dependency>
    <!-- ... -->
  </dependencies>
</project>

Step 2

Declare the xwiki.extension.javascript.modules.importmap property. See the ! at the start of the value and the _ at the start of the key.

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
   <properties>
     <xwiki.extension.javascript.modules.importmap>
     {
       "_module-id": "!my.group.id:my-webjar/index.prod.js"
     }
     </xwiki.extension.javascript.modules.importmap>
  </properties>
</project>

Final result

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <parent>
    <groupId>org.xwiki.platform</groupId>
    <artifactId>xwiki-platform-livedata</artifactId>
    <version>18.1.0-SNAPSHOT</version>
  </parent>
  <packaging>webjar-node</packaging>
  <artifactId>xwiki-platform-livedata-webjar</artifactId>
  <properties>
      <xwiki.extension.javascript.modules.importmap>
     {
       "_module-id": "!my.group.id:my-webjar/index.prod.js"
     }
  </properties>
  <dependencies>
    <dependency>
      <groupId>my.group.id</groupId>
      <artifactId>module-id</artifactId>
      <scope>runtime</scope>
    </dependency>
  </dependencies>
</project>