Question

This is really getting me:

for(var i=0; i<10; i++) {
   (function(x) {     //use a closure to hold the "i" value
       request(arg[x], function(n) {
          //do something with the data returned from $getJSON
          console.log(n);
       });
   })(i)  //is this syntax correct?
}

function request(argX, callback) {    //is this syntax correct?
     $getJSON(parameter) { 
         //get request result
         ... 
     }
     callback(); //after request() function is completed, trigger the callback function
                 //is this syntax right? 

}

The reason I am using the callback function is because I want to manipulating the result from getJSON, so I need to wait the request function to complete.

I also need to bound the callback function with the loop index “i” value.

I have played the syntax for quite a while, but how come nothing was returned from the console log? It seems the callback function was never executed or executed before $getJSON was completed.

I need expert’s help!

Answer 1

The getJSON call is asynchronous, so you would be calling the callback function before the response has arrived.

Also you have a code bloack after the call to getJSON. The code in that won’t get called after the result has arrived either, it’s just a separate block that runs after the call, and also before the result arrives.

Put the callback function as a parameter in the call to getJSON:

function request(argX, callback) {
  $getJSON(parameter, callback);
}