Pass third argument in `createDecorator` without modification

[downace]

Example: I want to write Static decorator which can be used to add non-reactive instance properties with initial value. Something like this:

const Static = () => {
    return createDecorator((opts, key, descriptor) => {
        descriptor.enumerable = false;
        const initialValue = typeof descriptor.initializer === 'function'
            ? descriptor.initializer()
            : undefined;
        const beforeCreate = function() {
            this[key] = initialValue;
        };
        (opts.mixins || (opts.mixins = [])).push({ beforeCreate });
    });
};

But descriptor is undefined because of these lines in createDecorator:

if (typeof index !== 'number') {
    index = undefined;
}

[ngfk]

As a workaround you could do something like this:

const Static = () => {
  return (target, key, descriptor) => {
    createDecorator(opts => {
      descriptor.enumerable = false;
      const initialValue = typeof descriptor.initializer === 'function'
          ? descriptor.initializer()
          : undefined;

      const beforeCreate = function() {
        this[key] = initialValue;
      };
      (opts.mixins || (opts.mixins = [])).push({ beforeCreate });
    })(target, key);
  };
};