Rewrite module and _modulePrefix

[tleunen]

I know this is a library initially for Facebook internal projects but instead of copying the script, I was trying to reuse what you did here and noticed something in the script rewrite-modules.

The default value for _modulePrefix is ./.

var modulePrefix = context.state.opts._modulePrefix || './';

I think the default value should be an empty string, because if you require an external module from your node_modules folder, you don't want to prefix it with ./.

For my needs, and because my project uses external modules, I would need the default to be an empty string, but because of the line above, you'll understand it's not possible.

If for your needs the default should stay ./, would at least be possible to check if the option is set?

[zpao]

That case is specifically to handle rewriting @providesModule requires, which we do assume end up all being relative, so we wouldn't change the default. I vaguely remember having a case where I wanted something to be unprefixed but then I just added the single case to the module map.

I had some confused comment trying to figure out what you were trying to do before I realized the actual problem - that '' is falsy so we're ignoring your default even though you specified it. Yea, that's a good catch and we should be checking for it being set.