avocado-old/packages/mixins/property.js

export function PropertyMixin(key, meta = {}) {

  if (!meta || 'object' !== typeof meta) {
    throw new TypeError(
      `Expected meta for Property(${
        key
      }) to be object. ${
        JSON.stringify(meta)
      } given.`
    );
  }

  return (Superclass) => {

    if (Superclass.prototype[key]) {
      throw new TypeError(`can't redefine Avocado property "${key}"`);
    }

    if ('identity' === meta.transformProperty) {
      meta.transformProperty = (key) => key;
    }
    else if (!meta.transformProperty) {
      meta.transformProperty = (key) => `${key}_PRIVATE_PROPERTY`;
    }

    meta.eq = meta.eq || function (l, r) {
      return l === r;
    }

    meta.get = meta.get || function(value) {
      return this[meta.transformProperty(key)];
    }

    meta.set = meta.set || function(value) {
      this[meta.transformProperty(key)] = value;
    }

    let metaDefault;
    if (null === meta.default) {
      metaDefault = null;
    }
    else if (undefined === meta.default) {
      metaDefault = undefined;
    }
    else {
      metaDefault = JSON.parse(JSON.stringify(meta.default));
    }

    class Property extends Superclass {

      constructor(...args) {
        super(...args);
        if (undefined !== metaDefault) {
          meta.set.call(this, metaDefault);
        }
      }

    }

    Object.defineProperty(Property.prototype, key, {
      enumerable: true,
      get: function() {
        return meta.get.call(this);
      },
      set: function (value) {
        const old = meta.get.call(this);
        meta.set.call(this, value);
        if (this.emit && !meta.eq.call(this, old, value)) {
          this.emit(`${key}Changed`, old, value)
        }
      },
    });

    return Property;
  }
}