I am trying to get my head around how Javascript function behaves. Is it a function or an object or both?
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possible duplicate of Is Function really an ObjectAndy E– Andy E2010-10-15 16:42:40 +00:00Commented Oct 15, 2010 at 16:42
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4 Answers
Functions in javascript are first-class objects. So they're both functions and objects.
Because they are first class objects, you can assign a variable to a function and give it properties, eg:
var addName=function(){};
addName.blah = 1;
If they weren't first-class objects you'd be limited to this syntax but you can do it both ways:
function addName(){}
2 Comments
T.J. Crowder
No "pretty much" about it. They are functions, and objects.
palswim
@Chad: No +1 for that. +1 would be to include a link explaining what "first class" means, since people like to throw that term around all over the place here. Or better yet, say that functions are first-class objects without using the term "first-class" (i.e. explain it in a way that normal people would understand: "Yes, Javascript lets you assign functions to variables and call the variables..")
It is both.
Everything is "data" in Javascript, including functions. I find this a good way to picture it:
var f = function() { alert('foo'); };
This is an assignment to a variable that's no different than if you'd written, say:
var f = new String('foo');
Either way, you can then write statements like f.bar = 'baz'; to assign properties to your object. The only difference is that the () operator (if you will) works only if the variable you have happens to be a function. f() makes sense if it's a function; f() makes no sense if it's a string or some other piece of data.
20 Comments
Šime Vidas
-1 expression statements (which the assignment is) should be terminated with a semi-colon.
T.J. Crowder
@Šime Vidas: Dude, by all means post the comment, but isn't the -1 a bit harsh for something that A) Is off-topic, and B) Is allowed by the language (even though relying on it is a really, really bad idea)?
Šime Vidas
Also, you cannot assign properties to variables that contain primitive values.
T.J. Crowder
@Šime Vidas: I'm not VoteyDisciple.
Claudiu
You can do
var f = "foo"; f.bar = 4;. What happens is f in f.bar gets converted to a String, then its bar property is assigned, then the converted String value is lost since nothing has a reference to it. but you can do it =) |
In JavaScript all functions are objects.
Functions are objects that can be called. (They have a internal [[Call]] property)
Comments
Well, I'm not going to say "JavaScript functions are objects of first class", since everyone already said that, but if you want more on functions, take a look at this short page:
http://jqfundamentals.com/book/ch02s09.html
By the way, if you're planning on learning JavaScript and JQuery, that's a free online book for you.
1 Comment
authentictech
Always include relevant information from the cited article in your answer because, as in this case, web pages/sites can disappear.