Translate PHP String Functions to Javascript / jQuery

This is the PHP code I'm trying to translate into Javascript / jQuery. Any ideas?

$root_folder = 'es';
$url = "http://domainNamehere.com/event/test-event-in-the-future/";
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$p = strpos($url, '/', 8);
$url_new = sprintf('%s/%s/%s', substr($url, 0, $p), $root_folder, substr($url, $p+1));

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var root_folder = "es",
    url = "http://domainNamehere.com/event/test-event-in-the-future/",
    url_new = "",
    path_finder = /^(((http)s?:)?\/\/[^\/]+\/)/i;

url_new = url.replace(path_finder, "$1" + root_folder + "/");

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strpos() ~ .indexOf()
substr() ~ .substring()
sprintf() ~ +

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PHP.js offers ports of many common PHP functions to JavaScript.