Permutation JavaScript

<script type="text/javascript">
function getPerms(chars) {
    document.write('Calling getPerms("' + chars + '")<br />');
    if (chars.length === 1) {
        // BASE CASE
        document.write("Base case, returning " + chars + "<br />");
        return [chars];
    }
    // RECURSIVE CASE
    let permutations = [];
    let head = chars[0];
    let tail = chars.substring(1);
    let tailPermutations = getPerms(tail);
    tailPermutations.forEach(function(tailPerm) {
        document.write("For " + chars + " putting head " + head + " in all places in " + tailPerm + "<br />");
        for (let i = 0; i < tailPerm.length + 1; i++) {
            let newPerm = tailPerm.slice(0, i) + head + tailPerm.slice(i);
            document.write("New permutation: " + newPerm + "<br />");
            permutations.push(newPerm);
        }
    });
    document.write("All permutations of " + chars + " are " + permutations + "<br />");
    return permutations;
}

document.write("Permutations of \"ABC\":<br />");
document.write("Result: " + getPerms("ABC"));
</script>