Get common git sha ancestor between a sha and a branch

gistfile1.js

getCommonAncestor: function(headSha, baseBranch) {
    return new Bluebird(function(resolve) {
      var command = "bash -c 'diff -u <(git rev-list --all " + headSha + ") "+
      "<(git rev-list --first-parent " + baseBranch+")' "+
      "| sed -ne 's/^ //p' | head -1";

      execute(command, function(data) {
        resolve(data);
      });
    });
  }