int selectionStart

Source 

@DomName('HTMLTextAreaElement.selectionStart')
@DocsEditable()
int get selectionStart =>
    _blink.BlinkHTMLTextAreaElement.instance.selectionStart_Getter_(this);
void selectionStart=(int value)

Source 

@DomName('HTMLTextAreaElement.selectionStart')
@DocsEditable()
set selectionStart(int value) => _blink.BlinkHTMLTextAreaElement.instance
    .selectionStart_Setter_(this, value);