How to get 'this' value of caller function?

If I have a function like this:

function foo(_this) {
    console.log(_this);
}

function bar() {}
bar.prototype.func = function() {
    foo(this);
}

var test = new bar();
test.func();

then the test instance of bar gets logged.

However, for this to work I have to pass the this in the bar.prototype.func function. I was wondering whether it is possible to obtain the same this value without passing this.

I tried using arguments.callee.caller, but this returns the prototype function itself and not the this value inside the prototype function.

Is it possible to log the test instance of bar by only calling foo() in the prototype function?