JSFiddle - React, Tailwind, and code Playground

JavaScript

$.when(checkAvailability())
   .then(getWebTree())
   .fail(function(message){
       if(message === 'Not available!')
       {
           // do stuff
       }
   });

function checkAvailability(){
    var dfd = $.Deferred();
    
    $.ajax({
    url: '/echo/html/' /*SERVERURL+'index.php/home/checkAvailability'*/,
    data: {
        html: "unavailable"
    },
    type: 'POST',
    datatype: 'text',
    success: function(data){              
        if(data == 'unavailable'){
            dfd.reject("Not available!");
        }
        else{
           dfd.resolve();
        }
    }
    });
    
    return dfd.promise();
};

function getWebTree(){
    $.ajax({
        url: '/echo/json/' /*SERVERURL+'index.php/home/getWebTree/'*/,
        dataType: 'json',
        success: function(data){
            console.log("getWebTree success");
        }
    });
};