Plug-in GPL and JS

I want to develop a WP plug-in. I just read this old post in Stackoverflow

only the PHP code in a plugin has to be GPL’ed – you can distribute any files which don’t contain PHP which interacts with WordPress under a separate license to forbid redistribution. For example, CSS, JavaScript, and images don’t have to be under the GPL.

Is any of this still true? For e.g., is the JS file of my plugin now also under GPL? I cannot find anything newer that specifically addresses this issue in the WP documentation. Thanks.

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