code: function render (name, data, options, callback) {
    options = options || {}
  
    var engine = getInstance(objectAssign({}, options, {
      name: path.normalize(name),
      extname: path.extname(name)
    }))
  
    if (typeof callback === 'function') {
      return engine.render(data, options, callback)
    }
  
    return new Promise(function (resolve, reject) {
      engine.render(data, options, function (err, content) {
        if (err) return reject(err)
        resolve(content)
      })
    })
  }
docs: main