Get base branch name of current pull request raised

getBaseBranchName.js

/*
 * Only works if github cli is installed and logged in
 */
function getPRDetails() {
  exec("gh pr view").then(
    stdout => {
      const response = stdout.toString();
      const prDetails = response.match(/into (\S+) from (\S+)/i);
      const [, baseBranch, targetBranch] = prDetails;
      console.log("Base branch: ", baseBranch);
      console.log("Target branch: ", targetBranch);
    },
    err => {
      console.log("Failed to fetch PR details. Install Github CLI in order to get base branch / No open PR for this branch");
    }
  );
}

Could you help with how you're using the exec command with .then?
I tried using a promise and shelljs exec (also child_process exec) but the command gh pr view gives different output when I ran it on terminal vs in the script.