Warn when using a minified copy of dev React

[sophiebits]

Fixes #4842.

[syranide]

Idea; since you actually enable name mangling and optimizations separately, what about checking (function() { 0; }).toString().indexOf('0') !== -1 (or return 0+0 and test for +). In the end it doesn't really matter, just thought I'd bring it up.

[gaearon]

Oh, that's smart.

[jimfb]

@syranide Haha, interesting. In theory, a good optimizer would replace (function() { 0+0; }).toString().indexOf('+') !== -1 with true. But I suspect that's an academic discussion, since I can't think of how detecting optimizations adds much value on top of detecting minification.

[syranide]

@jimfb That applies to the original code as well. It would also be an invalid optimization as toString could have been overloaded elsewhere.

[jimfb]

👍

[lijunle]

Hi, the short URL https://fb.me/react-minification does not redirect to something meaningful now. There is not download page now.

[sophiebits]

I updated the URL to point somewhere more relevant.