JSFiddle - React, Tailwind, and code Playground

JavaScript

var v = 20; // Variable part of search query
    var str = "The rain 20 in SPAIN stays mainly in the plain"; // String to search
    var n = str.match('ain ' + v); // The searching, returns null if not found or the matches found. Notice the 'ain' string has been added (this can of course be changed)
    
    if(n != null){
       alert(n + ' found!');
    }else{
       alert(v + ' not found...');   
    }