A snippet using the github public api to get the url and sha of the first commit for a given repo

Get the first commit url.js

// A snippet using the github public api to get
// the url and sha of the first commit for a given repo
function openFirstCommit(userorg, repo) {
  return fetch('https://api.github.com/repos/'+userorg+'/'+repo+'/commits')
    // the link header has additional urls for paging
    // parse the original JSON for the case where no other pages exist
    .then(res => Promise.all([res.headers.get('link'), res.json()]))
    
    .then(([link, commits]) => {
      if (link) {
        // the link contains two urls in the form 
        // <https://github.com/...>; rel=blah, <https://github.com/...>; rel=thelastpage
        // split the url out of the string
        const pageurl = link.split(',')[1].split(';')[0].slice(2,-1);
        // fetch the last page
        return fetch(pageurl).then(res => res.json());
      }
    
      // if no link, we know we're on the only page
      return commits;
    })
  
    // get the last commit and extract the userpage url
    .then(commits => commits[commits.length-1].html_url)
  
    // navigate there
    .then(url => window.location.href = url);
}

function go() {
  const [, userorg, repo] = window.location.pathname.split('/');
  return openFirstCommit(userorg, repo);
}