Using a 'required' validator such as below, I'm able to get past the validation by just entering a space (or multiple spaces).

This differs from the default jQuery MVC + Unobtrusive behaviour where spaces are treated as an empty string and fail validation.

<input data-val="true" data-val-required="Field cannot be blank." id="FieldName" name="FieldName" type="text" />

I think it is this line;

  return Boolean(value);

Which could be reworked as;

  return Boolean(value?.trim());

Link to source;

https://github.com/haacked/aspnet-client-validation/blob/062c8433f6c696bc41cd5d6811c840905c63bc9c/src/index.ts#L151C1-L151C31

I can do a pull request if you agree that it's correct.

Thanks both of you for your work on this.

Ryan