How to correctly handle the change() event?

Question

css

Tell me, I want to make an input in which you can enter values ​​​​for the text size font-size and which will automatically set such a css text property
on the input when changing the field, hung this event onchange = "func (this. value);
and the function is this
function func (newfsize)
{
$("p").css("font-size", function(newfsize){
return newfsize;
});
}

This function for all paragraphs, which value I did not enter, sets font-size 3px; Tell me how it is implement more correctly, no matter how jquery or js.

Answer 1

https://jsfiddle.net/wq9qr4Lr/2/