JSFiddle - React, Tailwind, and code Playground

JavaScript

var rooter = {
    user: {
        firstName: 'Billy',
        lastName: 'Moon',
        arbitrary: {
            namespace: {
                height: '1.4m'
            }
        }
    }
}


var name = "user.lastName";

function access(obj, prop, defVal) {
    var objectNames = prop.split(".");

    var curObj = obj;

    for (var i = 0, len = objectNames.length; i < len; i++) {
        curObj = curObj[objectNames[i]];
        if (typeof curObj === 'undefined') {
            return defVal;
        }
    }
    return curObj;
}
alert(access(rooter, name));