JSFiddle - React, Tailwind, and code Playground

JavaScript

function test() {
    var myParam = "one"
    if (false) {
        var myParam = "two";
    }
    alert(myParam);
}
test(); // alert "one"


function testAjax() {
    var myParam = "one";
    $.ajax({
        url:    "http://url-to-get-error",
        error:  function(){
            if (false) {
                var myParam = "two";
            }
            alert(myParam);
        }
    }); 
}
testAjax(); // alert "undefined"