*******************************
   TypeScript Exceptions
*******************************

TypeScript exceptions are generated as TypeScript ``Error`` type descendants.

**Igor**:

.. code-block:: Igor
    
    exception AccessDenied
    {
        string user;
        string data_key;
        string reason;
    }

**TypeScript**:

.. code-block:: TypeScript

    export class AccessDenied extends Error {
        user!: string;
        dataKey!: string;
        reason!: string;

        constructor() {
            super('AccessDenied');
            Object.setPrototypeOf(this, new.target.prototype);
        }
    }

See https://github.com/Microsoft/TypeScript/wiki/Breaking-Changes#extending-built-ins-like-error-array-and-map-may-no-longer-work why setting prototype explicitely is required.

.. _ts_error_message:

Setting Error Message
========================

By default exception class name is used as error message. This behavior can be altered by marking one of string fields with ``error_message`` attribute. 
Then this field value is treated and stored as ``Error.message``.

**Igor**:

.. code-block:: Igor
    
    [* json.enabled]
    exception AccessDenied
    {
        string user;
        string data_key;
        [ts error_message]
        string reason;
    }

**TypeScript**:

.. code-block:: TypeScript

    export class AccessDenied extends Error {
        user!: string;
        dataKey!: string;

        constructor() {
            super();
            Object.setPrototypeOf(this, new.target.prototype);
        }

        static fromJson(json: Igor.Json.JsonValue): AccessDenied {
            const jsonObject = json as Igor.Json.JsonObject;
            const obj = new AccessDenied();
            obj.user = jsonObject['user'] as string;
            obj.dataKey = jsonObject['data_key'] as string;
            obj.message = jsonObject['reason'] as string;
            return obj;
        }

        static toJson(value: AccessDenied): Igor.Json.JsonValue {
            const result: Igor.Json.JsonObject = {};
            result['user'] = value.user;
            result['data_key'] = value.dataKey;
            result['reason'] = value.message;
            return result;
        }

        toJson(): Igor.Json.JsonValue {
            return AccessDenied.toJson(this);
        }
    }

Note, that reason field is not generated anymore. Instead, ``message`` is used as a value source for json serialization.