function in_array (needle, haystack, argStrict) {
    var key = '', strict = !!argStrict;

    if (strict) {
        for (key in haystack) {
            if (haystack[key] === needle) {
                return true;
            }
        }
    } else {
        for (key in haystack) {
            if (haystack[key] == needle) {
                return true;
            }
        }
    }

    return false;
}

var a_attack    = [838, 839, 840, 841, 842, 843, 844, 845];
var a_expire    = [846, 847, 848, 849, 850, 851, 852, 853, 854, 855, 856];

if(in_array(id_item,$.merge(a_attack, a_expire))){
    alert('TEEETAS!');
}