get variable value in callback function

Question

I have one callback function

function QueryKeyword(keyword, site, callback) {
  var querykeyword = keyword;
  var website = site;

  $.ajax({
    url: "http://www.test.com",
    jsonp: "jsonp",
    dataType: "jsonp",
    data: {
      Query: querykeyword
    },
    success: callback
  });
}

I am calling this function with in for loop like this :

for (i = 0; i < questionTerm.length; i++) {
  for (j = 0; j < site.length; j++) {
    var searchTerm = questionTerm[i] + ' ' + $('#search').val();

    QueryKeyword(searchTerm, site[j], function(reslt) {
      // I need to get j variable value here
      console.log(j);
    });

  }

}

Now I need to get "j" variable value in function see I console the j variable value but it does not get the j variable value.

Would you please let me know how I can fetch the value in this.

Thanks in advance

Answer 1

The problem is, that at the moment of your callback, j was reassigned multiple times to something different.

There are a few options you could do.

1. call your callback with the params you need

 function QueryKeyword(keyword, site, index, callback) { // ... $.ajax( success: function(result) { // call the callback with a second param (the index j) callback(result, index); } ) } QueryKeyword(searchTerm, site[j], j, function(reslt, param) { // param is j console.log(result, param); }); 

2. save the var in a closure

 (function() { var value = j; ... })(); 

3. use forEach

 questionTerm.forEach((term, i) => { site.forEach((s, j) => { // we are in a closure, // j will be correct here. QueryKeyword(term, s, function(reslt) { // j is still correct here console.log(j); }); }) }); 

4. if you use es6, you could use let keyword. Here is some good explanation, how it works when using for loops

 for(let i = 0; i < 10; i++) { console.log(i); setTimeout(function() { console.log('The number is ' + i); },1000); } 

Answer 2

You have to pass it in separately:

definition

function QueryKeyword(keyword, site, index, callback)
{
   ...
}

execution

QueryKeyword(searchTerm, site[j], j, function(reslt) {
   // I need to get j variable value here
   console.log(j);
});