I am getting an error at $deferred.promise(); about "'unknown' is not assignable to type 'string'". Can I set this to a string?

Error   TS2322  (TS) Type 'JQueryPromise<unknown>' is not assignable to type 'JQueryPromise<string>'.
  Type 'unknown' is not assignable to type 'string'.

this.cyclesService
  .compileCycle(cycle, allIndications, regimenPart.Cycles)
  .done((value) => {
    cycle.Sentence.CompiledText = value;
  });

public compileCycle(cycle: Models.Regimen.CycleModel, indications: Models.Indications.IndicationModel[], context: Models.Regimen.CycleModel[]): JQueryPromise<string> {
  var requestData = { Cycle: cycle, Indications: indications, Context: context };

  var $deferred = $.Deferred();

  $.ajax({
    async: true,
    type: 'post',
    data: JSON.stringify(requestData),
    contentType: 'application/json',
    url: this.apiUrls.CompileCycle,
  })
    .done((response) => {
      var value = response.Value;
      if (value.length > 0) {
        value = value.charAt(0).toUpperCase()   value.slice(1);
      }

      $deferred.resolve(value);
    })
    .fail(() => {
      $deferred.reject();
    });

    return

    $deferred.promise();
}

[HttpPost]
public IHttpActionResult CompileCycle([FromBody]CycleSentenceRequest request)
{
    request.Cycle.Sentence.Indications = request.Indications.ToList();
    request.Cycle.Sentence.Context = request.Context?.ToList();
    request.Cycle.Sentence.SequenceOrder = request.Cycle.SequenceOrder;
    return Ok(new { Value = request.Cycle.Sentence.CompiledText, ValueInContext = request.Cycle.Sentence.CompiledTextInContext });
}

CodePudding user response：

I believe the deferred object will have the correct type if it's instantiated like this:

var $deferred = $.Deferred<string>();
// now typeof $deferred.promise() is JQueryPromise<string>

Just by the way, this:

        return

    $deferred.promise();

essentially means this:

return undefined;
// $deferred.promise(); <- dead code, the method already returned

Please make sure you don't break the line right after the return statement.