Javascript - callback with objects -

i have problem callback function. want write function, can iterate object (i want use callback method), it's not working , don't know wrong this.

i'll glad help.

   services = [     {         name: "a",     },      {         name: "b"     }    ]     function service (data) {     this.name = data.name    }     function getdata (i) {     sample = new service(services[i])     console.log(sample)    }     getdata(0) /* function work*/     function getall(index, count, callback) {     service = new service(services[index]);     console.log(service)     if (index < count) {         callback(index + 1, count, getall)     }    }     getall (0, services.length, getall) /* function not working */ 

the error due calling services[2] doesn't exists. getall function below solves problem

   function getall(index, count, callback) {        if (index < count) {            service = new service(services[index]);            console.log(service)            callback(index + 1, count, getall)        }    }