public static Long parseWithJsFormat(final String string, final String format) {
        Long millis = null;
        if (string != null
                && string.trim().length() > 0
                && format != null
                && format.trim().length() > 0) {
            try {
                double res = MomentJs.nativeFromCustomFormatString(string.trim(), format.trim());
                if (res > 0) {
                    millis = (long) res;
                }
            } catch (final Exception e) {
                GWT.log(e.getMessage());
            }
        }

        return millis;
    }
Returns the date/time in local time. If the date string has no
timezone information it is assumed to be local time.
See https://momentjs.com/docs/#/parsing/utc/
stroom-core-client-widget/src/main/java/stroom/widget/customdatebox/client/ClientDateUtil.java