Download Builder emits jQuery-UI 1.13.3 custom causing Syntax error in MS WebBrowser control (IE11 mode)

[mlisowsk]

For custom jQuery-UI 13.3.3 packages generated by the Download Builder:

The minified jquery-ui.min.js throws a Syntax error in line 6 when used in the Microsoft WebBrowser control which is based on IE https://learn.microsoft.com/en-us/dotnet/desktop/winforms/controls/webbrowser-control-overview?view=netframeworkdesktop-4.8 .
The error is not present/triggered by:

• the non-minified file jquery-ui.js
• the prior version (1.13.2) minified jquery-ui.min.js.
• the full (uncustomized) download of jQuery-UI 1.3.3.

My analysis shows the syntax error is caused by the arrow function that was generated by the minifier, and which is unsupported on the WebBrowser control (and all versions of IE https://caniuse.com/arrow-functions ).
This build error did not exist on or before June 30, 2023.

Since jQuery-UI 1.13 is supporting IE the customized builds should not throw syntax errors.

[mgol]

Please provide concrete steps you need to take to hit the issue; the fewer steps, the better.

[mgol]

Never mind, I see it even on a full build. I agree, this should not be happening.

[mgol]

It turns out UglifyJS suddenly started outputting ES6 code even if the source didn't contain such constructs: mishoo/UglifyJS#5967. Apparently, there's no official flag to disable it.

jQuery has switched to swc which has a flag to specify the ES version, we should just switch the download builder to it.

We should also switch jQuery UI. The 1.14.x minified files are also using arrow functions because of this UglifyJS issue - and while IE is not supported there, I'd prefer the minified file to stay in ES5 as long as the unminified one remains in ES5.

[mgol]

PR: #630