Why do I have to enclose a function in another function?

Question

When I write a function in JSON, why do I have to enclose it inside an anonymous function?

This works:

$.ajax({
        type: 'POST',
        url: 'http://www.myurl.com',
        data: data,
        success: function(data) {
            alert(data);
        }
});

This doesn't work:

$.ajax({
        type: 'POST',
        url: 'http://www.myurl.com',
        data: data,
        success: alert(data)
});

Thanks

Answer 1

You can do that. You just using the wrong syntax .

The success property needs a function expression not a function() call (which then returns a value into success );

So

success: myfunction

instead of

success: myfunction()

Answer 2

In short, because you're executing alert() and trying to assign the result to the success callback, so this won't work (the result of alert() is undefined ). However you can do this:

$.ajax({
    type: 'POST',
    url: 'http://www.myurl.com',
    data: data,
    success: customFunc //*not* customFunc() which would call it
});

In this case customFunc will receive the same parameters as success passes, so it's signature should be: customFunc(data, textStatus, XMLHttpRequest) , though it can be a subset, for example customFunc(data) .