JSFiddle - React, Tailwind, and code Playground

JavaScript

var foo = { jon : {age: 'old',   feeling: 'sad' },
            jack: {age: 'young', feeling: 'happy'}
          };

var bar1 = { name: 'jon' };
var bar2 = { name: 'joy' }; 

alert(bar1.name in foo);
alert(bar2.name in foo);