JSFiddle - React, Tailwind, and code Playground
HTML
<p id='demo'>
</p>
JavaScript
var string = "Hi welcome to stack overflow"
var toSearch = "stack"
//case insensitive search
var result = string.search(new RegExp(toSearch, "i")) > 0 ? 'Matched' : 'notMatched'
document.getElementById("demo").innerHTML = result