JSFiddle - React, Tailwind, and code Playground

JavaScript

function foo() {console.log('foo');}
foo.prototype.bar = function() {console.log('bar');}


var fn = "foo.prototype.bar";
var ptr = fn.split('.');
var func = ptr.reduce(function(a, b){
    return a[b] ? a[b] : a;
}, window);

console.log(func);