I'm just trying to get my head around this function expression.
It seems that if I create a function expression (p) that seems to contain a function declaration, the function declaration a() returns undefined.
var p;
p = function a() { return 'Hello' }
typeof p; // returns 'function'
typeof a; // returns 'undefined'
Can anyone explain why this is the case?
And also please let me know if my terminology is off too.
It isn't a function declaration. It is a function expression that happens to have a name. The name does not create a variable, but you can see it on the object
quentin@raston ~ $ node
> var p;
undefined
> p = function a() { return 'Hello' }
[Function: a]
> typeof p; // returns 'function'
'function'
> typeof a; // returns 'undefined'
'undefined'
> p
[Function: a]
> p.name
'a'
>
name property of function instances is non-standard.It seems that if I create a function expression (p) that seems to contain a function declaration
No. It is a named function expression, which does not "contain" a function declaration. The name of the function expression is available as an identifier inside the function's scope (pointing to the function itself), and as the nonstandard name property.
You can think of it as an anonymous function.
The reason that this is valid is because the local function name a can be used within the function declaration for recursion, but is not valid outside of this scope.
https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Operators/function
a is in scope within the function, but not outside it, though. (Not my downvote, btw.)
function a() { return "Hello" } var p = a;if you need both, or don't specify the anonymous function with a name.