JavaScript: what's the difference between a function name & function reference?

Question

I'm reading the Google Maps API and it states that the:

"callback: The function to call once the script has loaded. If using the Auto-loading feature, this must specify a function name, not a function reference.

What's the difference been a JavaScript function name vs a function reference?

http://code.google.com/apis/ajax/documentation/#GoogleLoad

• Pointy: Can you provide a link to exactly where that documenation fragment is? Is it actually for the API itself, or is it for the Google javascript loader, or what? edit oh I found it.

Answer 1

function: function func() {}

function reference: func

function name: 'func'

Answer 2

A function name is a string ("alert"). A function reference is the function itself (alert).

• Teddyk: so it would be callback="function_name" ?
• Ignacio Vazquez-Abrams: If you're using auto-loading.
• Teddyk: Yes, I'm using auto-loading. So is * callback="function_name"* correct?
• Ignacio Vazquez-Abrams: If you're using auto-loading.
• Teddyk: Any idea why google.com/jsapi?autoload={modules:[{name:%22maps%22,version:3,{other_params:%22sensor=false%22,callback:%22function_name%22}]} doesn't work then?

Answer 3

The name of a function is a string such as 'foo' in this case:

function foo() {}

A reference to a function is any variable that is set to the value of the function itself (not the result of calling it).

Functions in Javascript can be anonymous - you can have a reference to a function that has no name.

var bar = function() {}

Answer 4

Nothing.

// f1 :: function name
function f1(a) { return a*a; } 
// f2 :: reference to an anonymous function
var f2 = function(a) { return a*a; } 
// f3 :: a reference to the first function
var f3 = f1; 
// these are equivalent. The second one calls into 
// a different actual function. 
f1(3); // 9
f2(4); // 16
f3(5); // 25

• Pointy: The question makes sense if you read the snippet of documentation in context.

Answer 5

Well, perhaps what that bit of documentation means to say is that the "name" it expects should be a string containing the name of a function, instead of a "bare" function name (which is a reference to a function) or a function instantiation/definition expression.

edit OK I see what the deal is. This really isn't a Google Maps thing, it's the Google Javascript loader toolkit. The API does indeed want a string, which makes perfect sense since the function you want to call is inside the code that you're loading, and therefore you can't have a reference to it from the calling environment.

google.load("feeds", "1", {"callback" : "someFunctionName"});

It would make no sense to write:

google.load("feeds", "1", {"callback" : someFunctionName});

because "someFunctionName" used like that — as a reference to something — could not possibly be a reference to the right function (if it's defined at all).

• Teddyk: so it would be callback=function_name or callback=function_name() ?
• Pointy: Neither: {callback: "function_name"}