自学node对异步调用不是很明白  

var config = require('../config');

var redis = require("mredis"),
    client = redis.createClient(config.redis_port, config.connection_redis);

client.set("1", "hello word!!", function (err, reply) {
    console.log(reply);
    client.expire('1', 1200);
});
client.set("2", "hello word2!!", function (err, reply) {
    console.log(reply);
    client.expire('2', 1200);
});
client.set("3", "hello word3!!", function (err, reply) {
    console.log(reply);
    client.expire('3', 1200);
});
client.set("4", "hello word4!!", function (err, reply) {
    console.log(reply);
    client.expire('4', 1200);
});

client.keys('*', function (err, reply) {
    var ccc='';
    var array =[ '3', '4', '1', '2' ];
    for (i = 0; i < array.length; i++) {

        client.get(array[i], function (err, ddd) {

            ccc+=ddd;
        });
    }
    console.dir(ccc);
});
代码是这样

我想最后for循坏结束后得到

hello word!!+hello word!2!+hello word!!3+hello word4!!

我应该怎么修改呢   
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