FireClosure

Download (Firefox 14 and upwards, with Firebug 1.10)

FireClosure is an experimental Firebug extension that allows you to access closed-over ("private") variables in JavaScript, without having to mess around with tedious breakpoints.

For instance, given the following code...

function A() {
    var priv = 0;
    this.getter = function() {
        return priv;
    };
    this.setter = function(x) {
        priv = x;
    };
}
a = new A;

... FireClosure makes getting the value of priv as easy as a.%priv.

You can also see the closures in various DOM views, under the subheading "(scoped variables)".

Caveats

• Firefox often optimizes away closures or variables. For debugging, you can temporarily add some evals around the relevant places in the code to make this less of a problem (also makes your code less performant).
• Some objects might have unexpected scopes. This is because non-function objects don't actually have scopes in the first place; the functionality is faked by using the first property with typeof === 'function' that appears on the object.

Building

To create the XPI, download Apache Ant and run ant in the project directory.