What is meant by “leaking” into global scope?

A while ago, I offered-up a JavaScript design pattern (the Module Pattern - see below) that I got from a John Resig example as part of a solution to someone’s question and I received the following comment:

“…that pattern is a bit over engineered and not that good. Still leaking into global-scope. and your not opening yourself to async loaders. But it is better then just ad-hoc coding !”

So…

If “leaking” into global scope means “your object gets appended to the browsers window (object)”…then everything already gets appended (globally):

This “leaks” into global scope:

window.jQuery

…just call: window.jQuery and it resolves as a function();

This “leaks” into global scope:

function HelloWorld() { alert(‘Howdy’); }

…just call: window.HelloWorld() and you will get ‘Howdy’.

This “leaks” into global scope:

var myVariable = 10;

…just call: window.myVariable and you will get 10

If the commenter is correct, then all the above “leak” into global-scope. So, personally, I don’t see a way NOT to “leak” into global-scope as even your form controls exists there (as well).

As such, here are my questions…

• What is meant by “leaking” into global-scope?
• Why is that bad?
• How do you avoid it?
• When wanting to create persistent custom-objects, why is the Module Pattern (below) bad?
• Design patterns let you encapsulate complex logic, is encapsulation suddenly bad simply because we’re writing in JavaScript?
• Or...is this commenter simply wrong?
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