walker.js

/*
  Copyright © 2018 Andrew Powell

  This Source Code Form is subject to the terms of the Mozilla Public
  License, v. 2.0. If a copy of the MPL was not distributed with this
  file, You can obtain one at http://mozilla.org/MPL/2.0/.

  The above copyright notice and this permission notice shall be
  included in all copies or substantial portions of this Source Code Form.
*/
const Container = require('postcss/lib/container');

const registerWalker = (constructor) => {
  let walkerName = `walk${constructor.name}`;

  // plural sugar
  if (walkerName.lastIndexOf('s') !== walkerName.length - 1) {
    walkerName += 's';
  }

  /* istanbul ignore next */
  if (Container.prototype[walkerName]) {
    return;
  }

  // we need access to `this` so we can't use an arrow function
  Container.prototype[walkerName] = function walker(callback) {
    return this.walkType(constructor, callback);
  };
};

Container.prototype.walkType = function walkType(type, callback) {
  /* istanbul ignore next */
  if (!type || !callback) {
    throw new Error('Parameters {type} and {callback} are required.');
  }

  // allow users to pass a constructor, or node type string; eg. Word.
  const isTypeCallable = typeof type === 'function';

  // eslint-disable-next-line consistent-return
  return this.walk((node, index) => {
    if ((isTypeCallable && node instanceof type) || (!isTypeCallable && node.type === type)) {
      return callback.call(this, node, index);
    }
  });
};

module.exports = { registerWalker };