Make buildExportAll generate pure ES5 code.

[benjamn]

The untransformed let keyword causes problems for older parsers. I understand using let instead of var ensures each getter function has its own binding for the KEY variable, but the same can be accomplished (with less code) using a .forEach callback function, and this way there's no need to worry about generating a unique name for the key variable.

[loganfsmyth]

I appreciate the effort, but as long as you have the block scoping transform enabled, it'll pretty much do this conversion for you automatically. We had a little regression between 6.6.0. and 6.6.3 that caused that to fail, but it is fixed now. I'm not sure what we'd gain by doing this.

[codecov-io]

Current coverage is 85.21%

Merging #3391 into master will decrease coverage by -0.34% as of 9acd33b

@@            master   #3391   diff @@
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  Files          217     217       
  Stmts        15873   15873       
  Branches      3410    3410       
  Methods          0       0       
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- Hit          13580   13526    -54
- Partial        670     723    +53
- Missed        1623    1624     +1

Review entire Coverage Diff as of 9acd33b

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[benjamn]

Thanks, I'll try upgrading.

As to what would be gained, it's less code and fewer new variables… but then again shouldn't buildExportAll be a babel-runtime helper anyway?

[benjamn]

Update: I'm finding that let still occurs in the generated code even with the block scoping transform enabled, though other transforms may be interfering somehow, since it does work when I pare the plugins down to just transform-es2015-modules-commonjs and transform-es2015-block-scoping.

I can try to get to the bottom of what's going on with my preset, but I worry you're going to have more regressions of this kind. Why not make this helper more robust?

[amasad]

I think we didn't do a great job on plugin composability in babel 6 so +1 for making them as robust and standalone as possible.

[hzoo]

I'm ok with doing this but we definetely need to figure out why it's not working when other transforms are included.