JSFiddle - React, Tailwind, and code Playground

JavaScript

function abc() {
    
}

if (typeof abc != 'undefined' && $.isFunction(abc)) {
    alert('abc exists');
} else {
    alert('abc does not exist');
}

if (typeof def  != 'undefined' && $.isFunction(def)) {
    alert('def exists');
} else {
    alert('def does not exist');
}