site/gatsby-ssr.js

import React from "react";
export function onRenderBody(
  { setHeadComponents, setPostBodyComponents }
) {
 setHeadComponents([
    <script
        key="head1"
        type="text/javascript"
        src="https://code.jquery.com/jquery-3.4.1.slim.min.js"
    />,
    <script
        key="head2"
        type="text/javascript"
        stc="https://code.jquery.com/jquery-3.4.1.js"
    />,
    <script
        key="postbody1"
        type="text/javascript"
        src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta.3/js/bootstrap.min.js" 
    />,
    <script
      key="activePage"
      dangerouslySetInnerHTML={{
        __html: `
        let curActive = [' ', ' ', ' '];
        if (document.location.pathname === '/about'){curActive[0] = 'active';}  
        if (document.location.pathname === '/projects/physics' || document.location.pathname === '/projects/education' || document.location.pathname === '/projects/math' || document.location.pathname === '/projects/software'){curActive[1] = 'active';}  
        if (document.location.pathname === '/partners'){curActive[2] = 'active';} 
        `
      }}
    />
  ]);

  setPostBodyComponents([    
  ]);

}