get a value in deep path from an object

getNested.js

<script id="jsbin-javascript">
let r = document.getElementsByTagName('script')[0];
// console.log(r);
function getNested (theObject, path, defaultValue) {
    try {
        separator = '.';
    
        return path.
                replace('[', separator).replace(']','').
                split(separator).
                reduce(
                    function (obj, property) { 
                        return obj[property];
                    }, theObject
                );
                    
    } catch (err) {
        return defaultValue ? defaultValue : undefined;
    }   
}
let firstChildNode = getNested(r, 'childNodes.1.ownerDocument.activeElement', {});
console.log(firstChildNode);
</script>