Javascript AJAX function returns undefined instead

问题:

I have a function that issues an AJAX call (via jQuery). In the complete section I have a function that says:

complete: function(XMLHttpRequest, textStatus)
{
    if(textStatus == "success")
    {
        return(true);
    }
    else
    {
        return(false);
    }
}

However, if I call this like so:

if(callajax())
{
    //  Do something
}
else
{
    // Something else
}

The first is never called.

If I put an alert(textStatus) in the complete function I get true, but not before that function returns undefined.

Would it be possible to pass a callback function to my callajax() method? Like:

callajax(function(){// success}, function(){// error}, function(){// complete});

回答1:

complete is a callback function. It will be invoked by the Ajax object - asynchronously! - when the operation is complete. There is no way for you to catch the callback's result, only the Ajax object could do that.

Your callajax() function - you're not showing that function but I assume it simply makes the Ajax call - can not return the call's result (= the response headers and body), as the call will not have been finished yet when you exit the callajax() function.

Update: It is also well possible to make synchronous AJAX calls. Thanks to @Andris for pointing this out. In jQuery, you need to set the async option to false: Docs here. However, even those use the standard callback functions as far as I can see, so your desired method of returning false or true may still not work.