How to write the result of document.write('34'); into a variable?

Question

JavaScript

The question is that I need to write the result of executing document.write('34'); into a variable, and I googled and didn't find how to do it.
document.write('34'); comes to me from the server, so I can't change it in any way.
UPD:
I understand that this is fundamentally wrong, but

var a = open(&quot;POST&quot;, &quot;http://meteo.swamp.ru/js.php&quot;, false); <br/>
alert(a);

Outputs: object DOMwindow
That is, does it work?

Answer 1

<script>
document.write = function(text) {
  alert(text);
}
document.write('34');
</script>

Answer 2

You can get the result as a simple string and extract the desired part of it as a substring.

Answer 3

I'm not familiar with js, but as an option, redefine
document.write = function(x) {return x;}
run the response through eval:
var x = eval (response)
and return the old write to its place.
It seems to be possible to do so.

Answer 4

If only numbers come in, it makes sense to use the parseInt or parseFloat function.