jQuery Deferred object callback args & dynamically building?

Question

I saw this code at the jQuery site :

 1:  var jqxhr = $.ajax( "example.php" )
        .done(function() { alert("success"); })
        .fail(function() { alert("error"); })
        .always(function() { alert("complete"); });

   2: // perform other work here ...

     // Set another completion function for the request above
   3:  jqxhr.always(function() { alert("second complete"); });

2 questions :

I heard that the callback functions arguments of success , error , complete being transferred to done , fail , always respectively.

So if I want to use the jqXHR obj in always callback , How can i know from where he came (error or success) - because the params order in the method signature is different !!!

//here it is at place 3

enter image description here

//here it is at place 1

enter image description here

I also heard that deferred objects help us to build the callback functions dynamically. (as we can see in '3:')

I don't understand why will I ever need it ? by the time I got the Section 3: - the ajax call has already been made and alerted completed. In what scenarios the section 3: comes into action?

If you're using Firefox and have Firebug you could use console.log(jqXHR) in the always function to see what you get. — Alex
– Alex, Commented Nov 7, 2011 at 8:31
complete() is not meant to perform operations where it matters if the request was successful or not but to perform generic actions such as cleaning up things, re-enabling a disabled button, etc. — ThiefMaster
– ThiefMaster, Commented Nov 7, 2011 at 8:42

ThiefMaster · Accepted Answer · 2011-11-07 08:45:01Z

1

complete() is not meant to perform operations where it matters if the request was successful or not but to perform generic actions such as cleaning up things, re-enabling a disabled button, etc.

However, you could check if the first argument === jqxhr (the return value of $.ajax) - if the check is true, you know there was an error.

answered Nov 7, 2011 at 8:45

ThiefMaster

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1 Comment

Royi Namir Over a year ago

you mean to check if its object type ? what about if i did return a json object from server ? how would i distinguish ?

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