webui: Fix timezone detection

[dave14305]

Ignore timezone text in parentheses which may include a dash in non-English languages and confuse the index logic.

Fixes RMerl#726

[dave14305]

You could also opt for the RegExp approach taken in John's fork.

john9527/asuswrt-merlin@f63f408

[RMerl]

Can you give me an example of the string that may trigger the issue?

[dave14305]

See https://www.snbforums.com/threads/allways-the-same-issue-with-ntp.70175/#post-662399

And Tue Mar 23 2021 14:58:29 GMT+0100 (közép-európai téli idő) from #726.
And Thu May 07 2020 22:28:01 GMT+0300 (Itä-Euroopan kesäaika) from https://www.snbforums.com/threads/timezone-difference-warning.63943/#post-580836

[gabortim]

Thank you!

Here is my version

function corrected_timezone() {
    let offsetString = "";
    const today = new Date();
    const offset = today.getTimezoneOffset();

    offsetString += offset <= 0 ? '+' : '-';                             // time zone offset sign
    offsetString += ((-1 * offset) / 60).toString().padStart(2, '0');    // hours
    offsetString += (Math.abs(offset) % 60).toString().padStart(2, '0'); // minutes

    if (timezone !== offsetString) {
        document.getElementById("timezone_hint_div").style.display = "";
        document.getElementById("timezone_hint").innerHTML = "* <#LANHostConfig_x_TimeZone_itemhint#>";
    }
}