Error mutation ("hello", "hey"

Tell us what’s happening:
Ayuda: No entiendo como me da error la mutation (“hello”, “hey”)

Your code so far

function mutation(arr) {
var a = arr[0].toLowerCase();
var b = arr[1].toLowerCase();

for (var i = 0; i < b.length; i++) {
    if (a.includes(b[i])) {return true} 
else {return false};

mutation(["hello", "hey"])

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/83.0.4103.106 Safari/537.36.

Challenge: Mutations

Link to the challenge:

you are checking only the first value of i, so only the first letter of the string.

a return will stop a function and return a value