@sitecore-jss/sitecore-jss/dist/esm/utils/is-server.js

This module is provided as a part of Sitecore JavaScript Rendering SDK. It contains the core JSS APIs (layout service) and utilities.

/**
 * Determines whether the current execution context is server-side
 * @returns true if executing server-side
 */
function isServer() {
    return !(typeof window !== 'undefined' && window.document);
}
export default isServer;