Simple javascript http library modeled after python

var request = function(obj, success, failure) {                                            
    success = success || function(){};                                                     
    failure = failure || function(){};                                                     
                                                                                           
    obj.method = obj.method || 'GET';                                                      
    obj.headers = obj.headers || {};                                                       
    obj.params = obj.params || {};                                                         
                                                                                           
    var req = new XMLHttpRequest();                                                        
                                                                                           
    var params = "";                                                                       
    Object.keys(obj.params).forEach(function(param, i) {                                   
        params = params + (i === 0 ? "?" : "&") + param + "=" + obj.params[param];         
    });                                                                                    
                                                                                           
    req.open(obj.method, obj.url + params);                                                
                                                                                           
    Object.keys(obj.headers).forEach(function(header) {                                    
        req.setRequestHeader(header, obj.headers[header]);                                 
    });                                                                                    
                                                                                           
    req.onload = function() {                                                              
        if (req.status == 200) {                                                           
            success(req.responseText);                                                     
        } else {                                                                           
            failure(Error(req.responseText));                                              
        }                                                                                  
    };                                                                                     
                                                                                           
    req.onerror = function() {                                                             
        failure(Error("Network Error"));                                                   
    };                                                                                     
                                                                                           
    req.send(obj.data);                                                                    
};