JSFiddle - React, Tailwind, and code Playground

JavaScript

var nestedObjectAssignment = function(obj, propString, value) {
    var propNames = propString.split('.'),
        tmpObj = obj;

    for (var i = 0; i < propNames.length; i++) {
        tmpObj = tmpObj[propNames[i]] = i !== propNames.length-1 ?  {} : value;  
    }
    return obj
}

var obj = nestedObjectAssignment({},"foo.bar.foobar","hello world");

console.log(obj);