Sign Up to our social questions and Answers Engine to ask questions, answer people’s questions, and connect with other people.
Login to our social questions & Answers Engine to ask questions answer people’s questions & connect with other people.
Lost your password? Please enter your email address. You will receive a link and will create a new password via email.
Please briefly explain why you feel this question should be reported.
Please briefly explain why you feel this answer should be reported.
Please briefly explain why you feel this user should be reported.
What are the pros and cons of function-level scope specifically in Javascript compared to block-level scope in languages like Java?
I would like to see examples of function-level scope usage that would be harder or impossible to implement using block-level scope.
The first example that comes to mind is: JavaScript’s handling of closures would be much more expensive if implemented with block-level scope.
When you enter a function in JavaScript, an object is allocated (well, a couple, but we’ll focus on one) that ends up being the “variable object” — that is, where all the arguments and local vars for that function call are held (as properties). It’s this object that the closure actually uses (not just the “symbols” it appears to use; that’s a common misconception). These objects are strung together in a chain, called the scope chain, which is used for resolving unqualified symbols.
Imagine how much more expensive that would be if every block introduced new scope.