JSFiddle - React, Tailwind, and code Playground

JavaScript

foo = {bar:'def', baz:(function(){})(), bif:'alsodef'};
console.log(foo);
for (var prop in foo) {
    console.log('prop: ', prop, ', foo[prop]: ', foo[prop], ', typeof foo[prop]: ', typeof foo[prop]);
}

console.log('foo.baz: ', foo.baz, ', typeof foo.baz: ', typeof foo.baz);

if ('baz' in foo) {
    console.log('"in" is not a foolproof way to test whether an object property is undefined.');
}