How to programmatically inspect the JavaScript scope chain?

In a JavaScript debugger, I can manually inspect the scope chain of a function. For instance, when executing foo() on this piece of code:

var x1 = "global";
var foo = (function main () {
    var x2 = "inside obj";
    return function internalFoo () {
        var x3 = "inside internalFoo";
        console.log (x1+','+x2+','+x3); // get the scopes
    };
})();
foo ();

and setting a breakpoint on the console.log, I see the following scopes:

Is there some means to do this programmatically?

How can I inspect what is defined at every scope level?