getFieldNames (excludeNode) {
    if (this.type === 'object') {
      return this.childs
        .filter(child => child !== excludeNode)
        .map(child => child.field)
    }

    return []
  }
Get all field names of an object
@param {Node} [excludeNode] Optional node to be excluded from the returned field names
@return {string[]}