The problem with mandatory conventions is that they represent a different kind of user hostility--you're not trusting the developer to make his own decisions about variable names.
To give an example, many CoffeeScript programmers do follow simple naming conventions to call out top-level variables, such as CamelCase for classes or ALL_CAPS for constants. When you follow these conventions, it's pretty easy to avoid naming collisions.
In certain cases, though, you want a top-level variable to be lowercase, perhaps for stylistic reasons. If your files are relatively small, it's pretty easy to check for naming collisions when you introduce top-level variables after the fact, so a developer might decide that the risk is acceptable, especially if there is good test coverage.
Another kind of user hostility is to optimize for safety at all costs. I don't think any scoping mechanism totally eliminates the possibility of bugs, but some schemes do err on the side of safety over convenience. There's nothing wrong with trading off convenience for safety, but, on the other hand, you can make judgment calls that convenience and/or simplicity of the scoping model outweigh the risk of naming collisions.
Obviously, I like CoffeeScript, so I think Jeremy's made the correct tradeoffs. All languages work a little different--JavaScript, CoffeeScript, Python2, Python3, and Ruby all have different rules--and none of them are perfect in all situations. In all of the languages, though, it's reasonably straightforward to write correct code once you adopt general good practices--be careful with your names, and understand the language's approach to scoping.
To give an example, many CoffeeScript programmers do follow simple naming conventions to call out top-level variables, such as CamelCase for classes or ALL_CAPS for constants. When you follow these conventions, it's pretty easy to avoid naming collisions.
In certain cases, though, you want a top-level variable to be lowercase, perhaps for stylistic reasons. If your files are relatively small, it's pretty easy to check for naming collisions when you introduce top-level variables after the fact, so a developer might decide that the risk is acceptable, especially if there is good test coverage.
Another kind of user hostility is to optimize for safety at all costs. I don't think any scoping mechanism totally eliminates the possibility of bugs, but some schemes do err on the side of safety over convenience. There's nothing wrong with trading off convenience for safety, but, on the other hand, you can make judgment calls that convenience and/or simplicity of the scoping model outweigh the risk of naming collisions.
Obviously, I like CoffeeScript, so I think Jeremy's made the correct tradeoffs. All languages work a little different--JavaScript, CoffeeScript, Python2, Python3, and Ruby all have different rules--and none of them are perfect in all situations. In all of the languages, though, it's reasonably straightforward to write correct code once you adopt general good practices--be careful with your names, and understand the language's approach to scoping.