There is a bug in the JavaScript custom exception constructor implementation.
This thrift custom exception :

exception CustomError {
  1: required ErrorCode code;
}

results to a constructor which takes a single JS Object with custom properties :

const CustomError = module.exports.CustomError = class extends Thrift.TException {
  constructor(args) {
    super(args);
    this.name = "CustomError";
    this.code = null;
    // ...

We can check it in the associated TypeScript typings :

declare class ZaapError extends Thrift.TException {
    public code: ErrorCode;

      constructor(args?: { code: ErrorCode; });
  }

The generated code gives the JS object to the constructor of Thrift.TException.
But the Thrift.TException constructor takes a single string argument :

exports.TException = TException;

function TException(message) {
  Error.call(this);
  Error.captureStackTrace(this, this.constructor);
  this.name = this.constructor.name;
  this.message = message;
};
util.inherits(TException, Error);

Giving this custom object to the TException (instead of a string) throws unwanted Thrift exceptions in TBinaryProtocol.prototype.writeStringOrBinary :

Exception has occurred: Error: writeString called without a string/Buffer argument: [object Object]

The fix is to give the name of the custom exception to the constructor of the inherited Thrift exception class (TException).

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