私作 Deferred 功能

$DFD_Observer.js

const $DFD_Observer = (($, START_CALLBACK, FINISH_CALLBACK) => {
    let Func_Faked = func => () => typeof (func) == "function" && func() || true;
    let $DFD_Faked = $.Deferred().resolve()
    let $DFD_Array = [];
    return $dfd => {
           $DFD_Array = $DFD_Array.filter($item => $item.state && $item.state() == "pending").concat($dfd || $DFD_Faked);
           $.when($.Deferred(Func_Faked(START_CALLBACK)).resolve(), ...$DFD_Array)
            .always(() => $DFD_Array.length <= 1 && $DFD_Array[0] == $DFD_Faked && Func_Faked(FINISH_CALLBACK)() || $DFD_Observer());
           return $dfd;
    }
})(jQuery);