on after off scroll window

on after off scroll window

hello, I would like to know how to activate the event scroll after off in the browser window

Heres is my source

$('#btn').click(function() {
        $(window).off('scroll');//This works
    });

But I need to activate the scroll after  keyup event

$('#txt').keyup(function(){
 $(window).on();
})

But the scroll event does not work anymore,
I tried with bind and unbind, but I get the same behaviour like this:

$('#btn').click(function() {
        $(window).unbind('scroll');//This works
    });

$('#txt').keyup(function(){
 $(window).bind('scroll');
})