fightResolve = (a, b) =>{
const arr = [a.toLowerCase(),b.toLowerCase()]
console.log(arr.join() === ['a','s'].join())
}
fightResolve('a','S')
либо так более универсально
fightResolve = (arr1, arr2) => {
return JSON.stringify(arr1).toLowerCase() === JSON.stringify(arr2).toLowerCase()
}
console.log(fightResolve(['a,b'], ['a', 'b']))