Allowing for stricter subsets in future versions
On Mon, Oct 27, 2008 at 7:11 PM, David-Sarah Hopwood <david.hopwood at industrial-designers.co.uk> wrote:
It may be necessary in future to add additional incompatible restrictions along similar lines to strict mode, for example to support the work on 'Secure ECMAScript'. In that case, it's very likely that code written in such a subset should turn on the "strict" restrictions if it is running on an ES3.1 implementation, plus the additional restrictions if it is running on some later version. To do that it would be necessary to say something like:
"use strict"; "use stricter";
which is ugly and redundant. The redundancy can be avoided by specifying, in ES3.1, that the strict literal that turns on strict mode only needs to start with "use strict". For example, in that case
"use stricter"; or "use strict+secure";
would be sufficient for code in the stricter subset. There is no significant down-side if such a subset turns out not to be needed.
In Redmond we adopted essentially this same idea, but with comma as the separator. Strict mode is indicated by an initial strict literal expression statement containing exactly
use strict
or a string literal expression statement beginning with exactly the prefix
use strict,
ES3.1 does not suggest any interpretation of the characters after the comma.
It may be necessary in future to add additional incompatible restrictions along similar lines to strict mode, for example to support the work on 'Secure ECMAScript'. In that case, it's very likely that code written in such a subset should turn on the "strict" restrictions if it is running on an ES3.1 implementation, plus the additional restrictions if it is running on some later version. To do that it would be necessary to say something like:
"use strict"; "use stricter";
which is ugly and redundant. The redundancy can be avoided by specifying, in ES3.1, that the strict literal that turns on strict mode only needs to start with "use strict". For example, in that case
"use stricter"; or "use strict+secure";
would be sufficient for code in the stricter subset. There is no significant down-side if such a subset turns out not to be needed.