javascript PAC 代码分析理解

function FindProxyForURL(url, host) {
    var PROXY = 'SOCKS5 127.0.0.1:9999;SOCKS 127.0.0.1:9999';
    if (isPlainHostName(host)) return 'DIRECT';
    if (/^\d+\.\d+\.\d+\.\d+$/g.test(host)) return 'DIRECT';
    var rules = [
        [
            'cn',
            'lan',
            'local',
            'xn--fiqs8s'
        ], [
            'sinaapp.com',
            'qunar.com',
            'yihaodian.com',
        ], [
            'baixing.com',
            'xiami.com',
        ], [
            'mydrivers.com',
            'alisoft.com',
            '51jobcdn.com'
        ], [
            'zhi.hu',
        ]
    ];
    var vhost = host.toLowerCase();
    var rules_len = rules.length;
    for (var j = 0; j < rules_len; j++) {
        var rule_list = rules[j];
        var rule_list_len = rule_list.length;
        for (var i = 0; i < rule_list_len; i++) {
            var rule_entry = rule_list[i];
            var rule_dot = '.' + rule_entry;
            if (vhost === rule_entry || vhost.indexOf(rule_dot, vhost.length - rule_dot.length) !== -1) {
                return 'DIRECT';
            }
        }
    }
    return PROXY;
}