JSFiddle - React, Tailwind, and code Playground

HTML

<div id="main" contenteditable="true">abc</div>

CSS

#main>div:has(br) {
    background-color:yellow;
}

JavaScript

$("#main").keyup(function (e) {
    if (e.which == 13) {
        doSomething();
    }
});
$("#main").on("click", "div:has(br)", function () {
    doSomething();
});
$("#main").on("paste", function () {
    setTimeout(function () {
        debugger;
        if ($('#main').children().last().children().last().has('br').length >0) {
            doSomething();
        }
    }, 100);
});

function doSomething(){
   alert("new line...");
}