Small JS function to output a timezone formatted ISO string

dateToLocalISOString.js

function dateToLocalISOString(date) {
    const tzOffsetMins = date.getTimezoneOffset();
    const tzString = (-tzOffsetMins*100/60).toString();
    let tzPrefix = "";
    if (tzOffsetMins === 0) {
        return date.toISOString()
    } else if (tzOffsetMins < 0) {
        tzPrefix = "+";
    } else {
        tzPrefix = "-";
    }
    return new Date(date.getTime() - (tzOffsetMins * 60 * 1000))
        .toISOString()
        .replace("Z", tzPrefix+tzString);
}