function ajax(name, cb){
        console.log('request:'+name);
        setTimeout(function(){
            console.log('response:'+name);
            cb && cb();
        }, Math.random()*3000);
    }

    function request(name){
        return function(cb){
            return function(){
                ajax(name, cb);
            }
        }
    }

    var httpArr = [];

    for(var i = 0; i < 5; i++){
        httpArr.push(request(i));
    }

    httpArr.reduce(function(a, b){
        return b(a);
    })();
    
    // 输出
    /*
    request:4
    response:4
    request:3
    response:3
    request:2
    response:2
    request:1
    response:1
    */

用promise，AngularJS的话用$q