Tools: ES6 minification on Safari 10 (macOS + iOS)-> SyntaxError: Cannot declare a let variable twice: 'a'.

[pdesjardins90]

Description

Both ES6-unbundled and ES6-bundled presets result in an app that fails at launch on iOS 10, but not on iOS 11. The ES5-bundled preset works fine.

Error
SyntaxError: Cannot declare a let variable twice: 'a'.
(And a bunch of others which seem to follow this one)

Versions & Environment

• polymer-build: 2.1.1
• node: 8.9.1
• Operating System: macOS 10.13.1

Steps to Reproduce

• polymer init -> polymer-starter-kit
• polymer build
• polymer serve build/es6-unbundled or build/es6-bundled
• Open an iPhone Simulator
• Navigate to localhost:8081, witness the white screen and see console for error

Expected Results

No error is thrown and app loads normally, as on iOS 11

Actual Results

White screen and a bunch of console errors

[pdesjardins90]

More specifically, it has to do with js minification => unminified versions of these presets seem to work

[pdesjardins90]

Any news on this? We have to serve an unminified version of our app to customers because of this (26% heavier).

[czellweg]

The same issue appears when opened in Safari, for both build/es6-unbundled and build/es6-bundled. build/es5-bundled works fine.

[pdesjardins90]

@czellweg Desktop Safari 10?

[czellweg]

Yes, desktop Safari 10.1.1. For now, we had to disable js-minification:

"builds": [
    {
      "preset": "es6-bundled",
      "js": { "minify" : false }
    }
  ]

Not satisfactory of course, yet it'll have to do for now.

[pdesjardins90]

As we have. I'll update the title for desktop and mobile

[justinfagnani]

This issue was moved to Polymer/polymer-cli#946

[justinfagnani]

I moved this because it's the CLI that actually handles minificiation by calling out to Babili.