The javascript interpreter here doesn't seem to recognize the '.includes()' string method. I've tested the same code in multiple browsers and it works fine. In the codewars window I get the error-message "Object does not have the includes method". Is this because Codewars uses an older JS interpreter?

Here's the function which works in all my browsers:

function isVowel(chr) {
var uma = String.fromCharCode(228);
var umA = String.fromCharCode(196);
var umo = String.fromCharCode(246);
var umO = String.fromCharCode(214);
var umu = String.fromCharCode(252);
var umU = String.fromCharCode(220);
var vowels = "aeiouAEIOU" + uma + umA + umo + umO + umu + umU;
var ch = "" + chr;
return vowels.includes(ch);
}