JSFiddle - React, Tailwind, and code Playground

JavaScript

var id = "test1";

$.post("http://fiddle.jshell.net/echo/json/", {"data": "data"}, function(a) {
     alert(id); // will throw undefined
    
     var id = "test2";
    alert(id);
});

setTimeout(function() {
    $.post("http://fiddle.jshell.net/echo/json/", {"data": "data"}, function(a) {
         alert(id); // will throw "test1" as expected
        
         id = "test2";
        alert(id);
    });
}, 1000);