jQuery HOW TO?? pass additional parameters to success callback for $.ajax call?

Question

I am trying, in vain it seems, to be able to pass additional parameters back to the success callback method that I have created for a successful ajax call. A little backgro

Answer 1

this is Out of Scope

Just so you (or anyone else) understand(s)¹, the reason that this was undefined in loadImagesInSelect() in your original example was because that function was under a different scope, and scopes don't "cascade" like that².

When you specified a "context" of selectBox in your AJAX call, it set the context (this) for the functions given to "success" and "error". (It just so happens that they were both anonymous functions.) At this point, this is defined in both of these functions, as the value of selectBox. Now, in the function passed to "success", you call loadImagesInSelect(). When you call a function, it creates a new scope. In this scope, this will be window in non-strict mode and undefined in strict mode.

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Put Graphically (in Strict Mode³):

// this = window (global scope)

$j = jQuery.noConflict();
function getImages(urlValue, selectBox) {

    // this = undefined (function scope level 1)

    $j.ajax({
        type: "GET",
        url: $j(urlValue).val(),
        dataType: "jsonp",
        context: selectBox,
        success: function(data) {

            // this = selectBox (function scope level 2)

            loadImagesInSelect(data);
        },
        error: function(xhr, ajaxOptions, thrownError) {

            // this = selectBox (function scope level 2)

            alert(xhr.status);
            alert(thrownError);
        }
    });
}

function loadImagesInSelect(data) {

    // this = undefined (function scope level 3)

    var select = $j(this);
    select.empty();
    $j(data).each(function() {
        var theValue = $j(this)[0]["@value"];
        var theId = $j(this)[0]["@name"];
        select.append("" + theValue + "");
    });
    select.children(":first").attr("selected", true);
}

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$.proxy() is Redundant

The use of $.proxy() in your updated code is redundant. You use $.proxy() to get this to the function that was formerly called loadImagesInSelect(), but you moved that function up into "success" anyway (instead of calling it from within "success"). It already has access now to the value of this specified by "context".

You could remove the $.proxy() wrapper around your "success" function in your updated code and it would still work.

I know it's been years since you asked your question, but I hope this helps.

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1. I hope this doesn't come across as condescending; it's not meant to be.
2. At least, not when you call a function, and not with context. If you define a function within a function (i.e. a closure), then any variables in the outer function will be available in the inner function. However, the outer function's context (the this variable) still isn't available in the inner function.
3. Replace undefined with window for non-strict mode.
4. Or the native Function.prototype.bind() in ECMAScript 5.