Question

I’m doing a batch of getJSON() calls within a loop.

When the calls succeed the JSON returned contains a value equal to the loop counter, but when the error handler is called I can’t seem to figure out a way to to find out which query caused it (which value the loop counter had for the failed call).

var p;
for (p = 1; p <= pagecount; p++) {
  var params = {
    page:     p,
    pagesize: 100
  };

  $.getJSON("http://api.travel.stackexchange.com/1.1/tags?jsonp=?",
    params,
    function(data) {
      /* I can use data.page to know the value of page in the query */
    }
  ).error(function(jqXHR, textStatus, errorThrown) {
    /* how can I find the value "page" had in the query? */
  });
}

Answer 1

Generate a closure for each error callback:

function errorHandler(page) {
    return function (jqXHR, textStatus, errorThrown) {
        console.log(page); // it works
    };
}

for (var p = 1; p <= pagecount; p++) {
    var params = {
        page: p,
        pagesize: 100
    };

    $.getJSON("http://api.travel.stackexchange.com/1.1/tags?jsonp=?",
              params,
              function(data) {

    }).error(errorHandler(p));
}