Blocks in JavaScript do not create scopes. This is different from many other languages (like Java or C).

In fact, Crockford has mentioned this as well: http://javascript.crockford.com/code.html

"JavaScript does not have block scope, so defining variables in blocks can confuse programmers who are experienced with other C family languages."

Which is why this code works:

(function() {

    for (var i=0; i<100; i++);

    alert(i);

})();

Notice the variable `i` is accessible from outside the for-loop.

That's correct. Thanks a lot. Updated the blog with the correct example (using function). I was testing on Chrome and even your examples showed better results with value of variable 'a' to 1000, although slightly. Firefox shows no difference.

Another thing, JavaScript 1.7 has introduced block level scopes.. you can achieve that by using the 'let' keyword instead of 'var' to declare a variable. Although most browsers don't support it yet.

No problem. It's one of those things developers don't realize when coming from C-style languages. :)