JSFiddle - React, Tailwind, and code Playground
HTML
<input type="text" id="input1" data-site="site.ru" data-rubric="catalog" data-pages="1-15">
<input type="text" id="input2">
JavaScript
input1.addEventListener('input', function(e) {
var site = e.target.dataset.site;
var rubric = e.target.dataset.rubric;
var pages = e.target.dataset.pages;
var str = site + '/' + rubric + '/' + e.target.value + '/' + pages;
input2.value = str;
if(e.target.value) {
input2.value = str;
}else {
input2.value = '';
}
})