How to Check If Two Arrays Are Equal in JavaScript

function equalCheck(array1, array2) {
    if (!Array.isArray(array1) || !Array.isArray(array2)) {
        return false;
    }

    else if (array1 === array2) {
        return true;

    }

    else if (array1.length !== array2.length) {
        return false;

    }

    else {
        for (let i = 0; i < array1.length; ++i) {
            if (array1[i] !== array2[i]) return false;
        }
        return true;
    }
}

a1 = [1, 2, 3, 4];
a2 = [4, 3, 2, 1, 9];
console.log(equalCheck(a1.sort(), a2.sort()));