selectize-plugin-copy.js

import Selectize from 'selectize';

// https://gist.github.com/mdamien/a0f2bd91750a2d45c8ab
function copyToClipboard(text) {
    const el = document.createElement('textarea');
    el.style.position = 'absolute';
    el.style.left = '-9999px';
    el.setAttribute('readonly', '');
    el.value = text;

    document.body.appendChild(el);
    el.select();
    const success = document.execCommand('copy');
    document.body.removeChild(el);
    return success;
}

Selectize.define('copy_selection', function() {
    this.onKeyDown = (() => {
        const original = this.onKeyDown;
        return function(e) {
            const res = original.apply(this, arguments);

            const KEY_C = 67;
            if (e.keyCode === KEY_C && this.isCmdDown) {
                let selection = this.$activeItems
                    .map(x => $(x).data('value'))
                    .filter(x => x);

                // remove duplicates
                selection = Array.from(new Set(selection));

                copyToClipboard(selection.join(this.settings.delimiter || ' '));
                this.focus();
            }
            return res;
        };
    })();
});