JSFiddle - React, Tailwind, and code Playground

JavaScript

var potentialmodels = {
    "maddiekeller": {
        "firstname":"Maddie",
        "lastname":"Keller"
        },
    "rickbross": {
        "firstname":"Rick",
        "lastname":"Bross"
    }
}

var nameArray = Object.keys(potentialmodels).map(function(model) { return potentialmodels[model].firstname });

alert(nameArray);