Keyup handler for input editing

input-selector.directive.ts

@HostListener('keyup', ['$event']) onKeyUp(evt: KeyboardEvent): boolean
{
  // test for singleton leading negative sign as first character
  const v: string = this._input.value;
  const n: number = v.length;

  // for now, allow a blank field as it is possible that the entire number could be deleted by backspace before
  // entering a new number
  if (n == 0) {
    return true;
  }

  // physical quantities may not be negative and a decimal is currently not allowed
  if ( (n == 1 && v == "-") || (evt.key == ".") )
  {
    this.hasError     = true;
    this._input.value = this._currentValue.toString();

    return true;
  }

  // check for most recent keystroke being an enter, which is currently the only way to indicate an edit
  const code: string = evt.code.toLowerCase();
  if (code == 'enter' || code == 'return')
  {
    if (!isNaN(+v) && isFinite(+v))
    {
      this.hasError      = false;
      this._currentValue = +v;

      // set 'edited' border color and emit the changed event
      this.borderColor = '#66CD00';

      this._changed.emit({id: this._currentID, value: +v});
    }
    else
    {
      this.hasError     = true;
      this._input.value = this._currentValue.toString();
    }

    return true;
  }

  this.hasError = !Validation.checkNumber(evt);

  if (this.hasError)
  {
    console.log( "error: ", this._currentValue );
    // indicate an error by replacing the bad input with the 'current' or last-known good value
    // this may be altered in a future release
    this._input.value = this._currentValue.toString();
  }

  return true;
}