Archive - 2016

This cool JS snippet implements enumerations for JS:

function makeEnum(idField, indexField) {
  idField = idField || 'id';
  indexField = indexField || 'index';

  var enumeration = [];

  // Standalone object is useful for Underscore collection method usage,
  // for example:
  // _.keys(MyEnum.dict);
  var dict = {};
  enumeration.dict = dict;

  // This method can be used as a callback of map method:
  // var objects = ids.map(MyEnum.get);
  enumeration.get = function(id) {
    return enumeration[id];
  };

  // Registers a new enumeration item.
  enumeration.register = function(instance) {
    instance[indexField] = enumeration.length;
    enumeration[instance[idField]] = instance;
    dict[instance[idField]] = instance;
    enumeration.push(instance);
    return enumeration;
  };

  // Maps enumeration as dictionary:
  // MyEnum.mapDict(function(value, key) { return ...; });
  //
  // This is a shorthand for the next Underscore expression:
  // _.chain(MyEnum.dict).map(function(value, key) {
  //   return [key, ...];
  // }).object().value();
  enumeration.mapDict = function(iteratee, context) {
    var result = {};
    for (var id in dict) {
      if (dict.hasOwnProperty(id)) {
        result[id] = iteratee.call(context || this, dict[id], id, dict);
      }
    }
    return result;
  };

  return enumeration;
}

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