How to convert an "object" into a function in JavaScript?

Question

JavaScript allows functions to be treated as objects--if you first define a variable as a function, you can subsequently add properties to that function. How do you do the reverse, and add a function to an "object"?

This works:

var foo = function() { return 1; };
foo.baz = "qqqq";

At this point, foo() calls the function, and foo.baz has the value "qqqq".

However, if you do the property assignment part first, how do you subsequently assign a function to the variable?

var bar = { baz: "qqqq" };

What can I do now to arrange for bar.baz to have the value "qqqq" and bar() to call the function?

Answer 1

It's easy to be confused here, but you can't (easily or clearly or as far as I know) do what you want. Hopefully this will help clear things up.

First, every object in Javascript inherits from the Object object.

//these do the same thing
var foo = new Object();
var bar = {};

Second, functions ARE objects in Javascript. Specifically, they're a Function object. The Function object inherits from the Object object. Checkout the Function constructor

var foo = new Function();
var bar = function(){};
function baz(){};

Once you declare a variable to be an "Object" you can't (easily or clearly or as far as I know) convert it to a Function object. You'd need to declare a new Object of type Function (with the function constructor, assigning a variable an anonymous function etc.), and copy over any properties of methods from your old object.

Finally, anticipating a possible question, even once something is declared as a function, you can't (as far as I know) change the functionBody/source.