JSFiddle - React, Tailwind, and code Playground

JavaScript

var obj = {
    Foo: {
        Bar: {
            xyz: 'Works!'    
        }
    }    
};

function defined( val, names ) {
    names = names.split( '.' );    
    while ( val && names.length ) { val = val[ names.shift() ]; }    
    return typeof val !== 'undefined';
}

document.write( defined( obj, 'Foo.Bar.xyz' ) );