JSFiddle - React, Tailwind, and code Playground

JavaScript

var foo = {
    "jon": {
        "age": "old",
        "feeling": "sad"
    },
    "jack": {
        "age": "young",
        "feeling": "happy"
    }
};
var bar = {
    "name": "jon"
};
function isMember(prop) {
    return foo.hasOwnProperty(prop);
}
console.log(isMember(bar.name));