rxjs - Discard future returning observables

Question

So here is my observable code:

  var suggestions =
        Rx.Observable.fromEvent(textInput, 'keyup')
          .pluck('target','value')
          .filter( (text) => {
              text = text.trim();
              if (!text.length) // empty input field
              {
                  this.username_validation_display("empty");
              }
              else if (!/^\w{1,20}$/.test(text))
              {
                  this.username_validation_display("invalid");
                  return false;
              }
              return text.length > 0;
          })
          .debounceTime(300)
          .distinctUntilChanged()
          .switchMap(term => {
              return $.ajax({
                type: "post",
                url: "src/php/search.php",
                data: {
                  username: term,
                  type: "username"
                }
              }).promise();
            }
          );
  suggestions.subscribe(
    (r) =>
    {
        let j = JSON.parse(r);
        if (j.length)
        {
            this.username_validation_display("taken");
        }
        else
        {
            this.username_validation_display("valid");
        }
    },
    function (e)
    {
        console.log(e);
    }
  );

The problem I have is when the input is empty I have a another piece of code that basically returns a 'error: empty input' but it gets overridden by the returning observable. So I was wondering if there was a way to disregard all observables if the text.length is 0, but also re-subscribe when the text length isn't zero.

I've thought about unsubscribe but don't know where to fit it in to try.

Answer 1

Maybe this would work? The idea is to incorporate empty input in the switchmap so the current observable is switched off i.e. discarded also in that case.

  var suggestions =
        Rx.Observable.fromEvent(textInput, 'keyup')
          .pluck('target','value')
          .filter( (text) => {
              text = text.trim();
              if (!text.length) // empty input field
              {
                  this.username_validation_display("empty");
              }
              else if (!/^\w{1,20}$/.test(text))
              {
                  this.username_validation_display("invalid");
                  return false;
              }
          })
          .debounceTime(300)
          .distinctUntilChanged()
          .switchMap(text=> {
              if (text.length > 0) {
              return $.ajax({
                type: "post",
                url: "src/php/search.php",
                data: {
                  username: text,
                  type: "username"
                }
              }).promise()}
              return Rx.Observable.empty();
            }
          );