Please help me to write this in javascript

jQuery is one of many JavaScript libraries. So it is essentially JavaScript. jQuery is optimized, lightweight, cross broswer and promote "write less do more". Take the second statement of your code as an example:

var firstResult =$(".pac-container .pac-item:first").text();

To reverse-engineer it in JavaScript would look like this:

var parent = document.getElementsByClassName("pac-container");
// assume there is only one element with class name = "pac-container"
for (var i = 0; i < parent[0].childNodes.length; i++) {
    if (parent[0].childNodes[i].className == "pac-item") {
         firstResult = parent[0].childNodes[i].innerText;
         break;
    }
}

So there is really no reason to reverse engineer except for some academic exercises, may be.
Read more: https://blog.udemy.com/jquery-vs-javascript/[^]