Decorate outbound link for cross domain tracking

gaLinkDecorator.js

const decorateLink = (destinationUrl) => {
    if (ga !== undefined && typeof ga.getAll === 'function') {
        const trackers = ga.getAll();
        if (trackers.length > 0) {
            const linker = new window.gaplugins.Linker(trackers[0]);
            return linker.decorate(destinationUrl);
        }
    }
    return destinationUrl;
}

// usage
// decorateLink('https://google.com')
// https://google.com?_ga=XXXX