JQuery Callback with arguments - newbie

Question

So, near the bottom the jQuery basic pages, it gives this example, NOTICE how the anonymous function() does not have params. Quote JQuery page says

The anonymous function does exactly one thing: calls myCallBack, with the values of param1 and param2 in the outer scope.

$.get('myhtmlpage.html', function(){
  myCallBack(param1, param2);
});

So, I gave it a try based on this example

My code is like this, similar thing, at line 10, I have an anonymous function(result), but I need to add the param "result" can't be just function() as suggested by JQuery website, or it won't work:

<html>
    <head>
        <script type="text/javascript" src="jquery.js"></script>
        <script type="text/javascript">
            $(document).ready(function () {
                var GetResults = function (result) {
                        $("div").html(result);
                    }
                $("button").click(function () {
                    $.get("demo_ajax_load.txt", function (result) {
                        GetResults(result);
                    });
                });
            });
        </script>
    </head>
    <body>
        <div>
            <h2>Let AJAX change this text</h2>
        </div>
        <button>Change Content</button>
    </body>
</html>

My question is, why does JQuery page says it will work with just function() without params? I have to add function(result) to make it work? Am I missing something?

The page may be worded wrong, especially if you want to work with what is returned. I think that demo shows that you can call other functions within the anonymous function. — Jay Blanchard
– Jay Blanchard, Commented Apr 20, 2012 at 14:00
Javascript does not require named parameters. You can pass an arbitrary amount of arguments into a function declared with no inputs. — Joe
– Joe, Commented Apr 20, 2012 at 14:00
@Tom jQuery.com has been updated and clarified. Thanks for your help! — Sampson
– Sampson, Commented Apr 20, 2012 at 14:46

Manse · Accepted Answer · 2012-04-20 14:08:15Z

7

The key is in the explanation on the link you posted :

The anonymous function does exactly one thing: calls myCallBack, with the values of param1 and param2 in the outer scope

This is basically saying that the param1 and param2 variables are defined previously (outer scope) :

$("button").click(function () {
    var param1 = "something";
    var param2 = "something else";
    $.get('myhtmlpage.html', function(){
       myCallBack(param1, param2); // this uses the previously declared variables
    });
});

Within JavaScript when you call a function myfunc("some text") for example the actual function could be defined as function myfunc(var1) { or function myfunc() { the first example just formally declares a variable name for the first argument ...

function myfunc() {
    alert(arguments[0]);
}

myfunc("some text");

arguments that are not formally declared ar available using the arguments array ... see this doc on MDN

edited Apr 20, 2012 at 14:08

answered Apr 20, 2012 at 14:01

Manse

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1 Comment

Tom Over a year ago

aww! i get it now. I am new to it and I was a bit confused :P Thanks heaps for the help.

Niet the Dark Absol · Accepted Answer · 2012-04-20 14:00:37Z

1

You need to have already defined the variables in order to use them inside a closure like that. Since the get function puts the result into the first parameter of the anonymous function, you need to put result there to catch it, if you want to do anything with it.

Try this: Remove the result parameter again, and add result="Hello World"; at the start of your code.

answered Apr 20, 2012 at 14:00

Niet the Dark Absol

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1 Comment

Tom Over a year ago

Thanks for the explanation! Now I refer back to the ajax api and the examples, I get the function signatures and the meaning of the examples!

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