Basics of the DeveloperFunction decorator

developer-function.ts

export const DEV_FUN_KEY = `DEVELOPER_FUNCTIONS`;
export function DeveloperFunction(opts: any) {
  return function(target: any, key: string) {
    const metaTarget = target.constructor;
    const developerFunctions = getOwnMetadata(DEV_FUN_KEY, metaTarget) || [];
    if (Array.isArray(opts)) {
      opts.forEach(opt => {
        developerFunctions.push({
          key,
          ...opt
        });
      });
    } else {
      developerFunctions.push({ key, ...opts });
    }

    defineMetadata(DEV_FUN_KEY, developerFunctions, metaTarget);
  };
}