Get git branch parent name in node.js

branch-parent.js

const { promisify } = require('util');
const { exec } = require('child_process');
const run = promisify(exec);

const normalizeString = string => (string || '').trim();

function getBranchParent () {
  return run(`git show-branch | grep '*' | grep -v "$(git rev-parse --abbrev-ref HEAD)" | head -n1`)
    .then(resp => {
      const commit = normalizeString(resp.stdout);
      const branchNameMatch = /\[(.*)\]/g.exec(commit);
      
      const parentBranch = (
        branchNameMatch
          ? branchNameMatch[1].replace(/\^|~./g, '')
          : 'HEAD'
      );
    
      return parentBranch;
    });
}

// bash: git show-branch | grep '*' | grep -v "$(git rev-parse --abbrev-ref HEAD)" | head -n1 | sed 's/.*\[\(.*\)\].*/\1/' | sed 's/[\^~].*//'