regexgen/src/map.js

Generate regular expressions that match a set of strings

/**
 * This ES6 Map subclass calls the getter function passed to
 * the constructor to initialize undefined properties when they
 * are first retrieved.
 */
class DefaultMap extends Map {
  constructor(iterable, defaultGetter) {
    if (typeof iterable === 'function') {
      defaultGetter = iterable;
      iterable = null;
    }

    super(iterable);
    this.defaultGetter = defaultGetter;
  }

  get(key) {
    if (!super.has(key)) {
      let res = this.defaultGetter(key);
      this.set(key, res);
      return res;
    }

    return super.get(key);
  }
}

module.exports = DefaultMap;