Issue When Transpiling / Minifying

[snuggs]

I think there is an issue with Uglify-JS or webcomponentsjs. As it's breaking our functionality in Safari at least within jsfiddle. https://jsfiddle.net/whdLtc5q/

[snuggs]

This only comes up when using minified es6. @pachonk care to test this out?

[grepsedawk]

Hmm, could I get more context to the issue?

…

On Wed, Aug 2, 2017, 8:00 AM snuggs ***@***.***> wrote: This only comes up when using minified es6. @pachonk <https://github.com/pachonk> care to test this out? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#78 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AGaPSx-jfC17sihvR4VpS9eY791fOAB4ks5sUHLUgaJpZM4OLfi6> .

[snuggs]

@pachonk check out the dist readme. It's in the minification step. Converting es6 to es5. I think our polyfill uses the same minifier thus creating the same tiny variable names e.

We use this https://github.com/paulovieira/UglifyJS2

[snuggs]

@pachonk to be clear i don't know what that first error is. That should cure half your queries. 😜

[snuggs]

@angelocordon @robcole @brandondees come to find out this was a bug in Safari. They have recently fixed it and is in current preview of Safari 11 (releasing in September). This is a good thing but requires someone to be forced to update. This bug still lingers for many people on safari who haven't updated. This is a perfect example of by leaning on the specs since they are "living" not every browser will always be at 100%. That being said the onus is on the PLATFORM VENDOR not the developer to update as in this case. The problem is happening when we minify ES6 -> ES6(minified with UglifyJS). I'll get this fixed up after I do a little research on the references. Luckily we have an unminified version that works fine and can use that in the mean time for Safari support. Thus (temporarily) fixing the initial issue @angelocordon and I first discovered.

Reference Links

• UglifyJS issue - [ES6] Safari: SyntaxError: Cannot declare a let variable twice r mishoo/UglifyJS#1753
• UglifyJS Pull Request - [ES6] fix safari syntax error - declare twice mishoo/UglifyJS#1851
• Webkit Bug - https://bugs.webkit.org/show_bug.cgi?id=171041
• Webkit changeset - https://trac.webkit.org/changeset/217200/webkit
• Glimmer (Ember.js) - github.com/ember build -e prod outputs JS that triggers Safari 10 bug "Cannot declare a let variable twice" glimmerjs/glimmer-blueprint#58
• Glimmer (Ember.js) - github.com/Safari 10 compatibility? glimmerjs/glimmer-application-pipeline#123

Fix for UglifyJS

safari10: true
https://github.com/mishoo/UglifyJS2/tree/harmony#mangle-options

Problematic UglifyJS Output

If you notice below the .assign (e, ...) is being shadowed by let e later within the function. The ECMAScript language has no issue with shadowing variables (We do this with Element vs window.Element)