JSFiddle - React, Tailwind, and code Playground

JavaScript

function exists(str, namespace) {
    var arr = str.split('.'),
        val = namespace || window;
  
    for (var i = 0; i < arr.length; i++) {
        val = val[arr[i]];
        if ( typeof val == 'undefined' ) return false;
    }
    return true;    
}


var x = {};
x.y = {};
x.y.z = 1;

alert( exists('x.y.z') );
alert( exists('x.y.z.foo') );