[BUG] Dash async causes syntax error in IE11

[shammamah-zz]

Thank you so much for helping improve the quality of Dash!

We do our best to catch bugs during the release process, but we rely on your help to find the ones that slip through.

Note - found while working on plotly/dash-core-components#627

Describe your context
Please provide us your environment so we can easily reproduce the issue.

• replace the result of pip list | grep dash below

dash                            1.6.0    
dash-core-components            1.5.0    
dash-dangerously-set-inner-html 0.0.2    
dash-flow-example               0.0.5    
dash-html-components            1.0.1    
dash-renderer                   1.2.0    
dash-table                      4.5.0    

• if frontend related, tell us your Browser, Version and OS

  • OS: Windows
  • Browser: Internet Explorer
  • Version: 11

Describe the bug

Using the dash-core-components library installed with the latest version of Dash that includes async (1.6.0) in an app causes the app to be stuck on "Loading..." and the following errors to show up in the console:

This is due to an arrow function:

Expected behavior

The components should render.

Screenshots

See above.

[Marc-Andre-Rivet]

Caused by /node_modules/, ^[@]plotly\/.*/ should be included as the non-transpiled source is used directly for the plugins.

This affects dash-renderer, html, dcc, table, bio, daq in production.
This affects the in-review changes:
plotly/dash-cytoscape#75
plotly/dash-canvas#29

[Marc-Andre-Rivet]

Also, there are other issues unrelated with async that are breaking IE11. Details in #1006

[Marc-Andre-Rivet]

Closed by #1006