[reissbaker]

I remember when it was generally suggested to avoid "use strict", because there wasn't great browser support. You could write "strict" code that would work at the time (due to browsers not actually enforcing strict mode), but in the future the same code might break in conformant releases of those browsers.

That said, these days it's invaluable. Getting errors early saves time and prevents subtle bugs. It's become a widely accepted best practice, as noted by other posters.

I definitely share your concerns about mode switches, but as long as there's a conformant implementation to test against, it seems like strong mode could move the language forward without too much of the "use strict" early adoption pain. Strict mode wasn't completely smooth sailing, but I think in the long run it helped.