currentIndex = 0;  
function ajax(){  
    if(currentIndex>=20){   
        return;  
    }  
    var url = ‘url‘;  
    console.log(i);  
    $.ajax({  
        type: ‘get‘,  
        url: url,  
        dataType: "json",  
        async: false,  
        cache: true,  
        success: function(json){  
            currentIndex++;  
            console.log("test");
            ajax();  
        },  
        error: function(data){  
            console.log("error...");  
            currentIndex++;  
            ajax();  
        }  
    });  
}