@atlaskit/adf-schema/dist/esm/schema/marks/to-json.js

Shared package that contains the ADF-schema (json) and ProseMirror node/mark specs

var OPTIONAL_ATTRS = ['title', 'id', 'collection', 'occurrenceKey', '__confluenceMetadata'];
export var toJSON = function toJSON(mark) {
  return {
    type: mark.type.name,
    attrs: Object.keys(mark.attrs).reduce(function (attrs, key) {
      if (OPTIONAL_ATTRS.indexOf(key) === -1 || mark.attrs[key] !== null) {
        attrs[key] = mark.attrs[key];
      }
      return attrs;
    }, {})
  };
};