A JavaScript function to check for newer versions using GitHub releases.

updateChecker.js

/**
 * This checks for newer releases on GitHub. If any newer versions can be found, it returns a promise resolving as the latest version tag. Otherwise the promise resolves as null.
 * @param {String} releaseTag The release tag of the code you implement this into.
 * @param {String} repo The repository containing the code.
 * @returns A Promise, resolving as the version tag if the provided release tag doesn't match the one provided on GitHub.
 */
const checkIfOutdated = (releaseTag, repo) => new Promise(async (resolve, reject) => {
  const releases = await fetch(`https://api.github.com/repos/${repo}/releases`).then(res => res.json());
  if(!Array.isArray(releases)) return reject();
  const latestRelease = releases[0];
  return resolve(latestRelease.tag_name === releaseTag ? false : latestRelease.tag_name);
});


/**
 * A short demonstration of how you could implement this to your own project.
 * 
 * In this example, if the latest release doesn't match v3.0, newerVersion will be the latest version tag. Otherwise it will be null.
 */
checkIfOutdated('v3.0', 'GeneTv/jubilant-happiness').then( newerVersion => {
  // NOTE: If during development, you provide a newer version than released on GitHub, this will also be detected as outdated. Either disable this during development or change the version tag in your code before you release the version.
  console.log( newerVersion ? `There is a newer version available: ${newerVersion}` : 'You are up to date.')
});