Closure scopes in JavaScript.

gistfile1.js

(function() {
    // This is a new closure. If things that happen here don't have side-effects on outside scope,
    // then whatever happens here will not be visible outside of it.

    (function() {
        // You can make closures inside of closure (inside of closures). Wee.
    })();
})();


// Unspecified scope defaults to the root scope (in browsers, that's `window`).
(function () {
    this === window;

    (function () {
        this === window;

        (function() {
            this === window;
        })();

    })();

})();


// Specifying scope using fn.call(...)
// See: https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Function/call
var myscope = {};
(function () {
    this === myscope;

    (function () {
        this === myscope;

        (function() {
            // There is no fn.call(...), so we get an unspecified scope
            // Note that scope does not get inherited from the parent closure.
            this === window;
        })();

    }).call(this);

}).call(myscope);


// Similar functionality can be achieved by binding scope to a variable.
(function () {
    // `this` #1
    var foo = this;
    var bar = 42;

    (function () {
        bar === 42;
        // `this` #2, but you can still use `foo` and `bar` from the previous scope.
        // You could even do `this = foo` if you're willing to live with yourself after doing that.
    });

})();


// More arbitrary scope
(function () {
    this === window;

    var foo = {'bar': 42};

    (function () {
        this === foo;
    }).call(foo);

})();