init.js

// The source of truth should be the element that initializes it.
// Have a default fallback

if ($multiSelect.length > 0) {
    $multiSelect.each(function () {
        let $this = $(this),
            dataset = $this.data(),
            options = defaults;
            
        // Since the number of options can vary,
        // non vital options that have no specified default
        // will be extracted from the dataset and added to options
      
        Object.entries(dataset)
            .map(property => options[property[0]] = property[1]);
        
        // We initialize the plugin with its
        // specific options for each instance
      
        $this.multiselect(options);
    });
}