JSFiddle - React, Tailwind, and code Playground

JavaScript

var urlValida = '/echo/html/';
var urlInválida =  '/NaoExiste/html/';

$.ajax({    
    type: 'GET',
    url: urlValida,
    success: function (data) {
        alert(urlValida + ' OnLine');
    }
}).error( function () {
        alert(urlValida + 'OffLine');
});

$.ajax({
    type: 'GET',
    url: urlInválida,
    success: function (data) {
        alert(urlInválida + ' OnLine');
    }
}).error( function () {
        alert(urlInválida + 'OffLine');
});