Every lawyer I consulted with always gave me the same answer: JavaScript in web page is code redistributed to whoever loads this page in their browser.
So yes, this is unambiguously redistribution.
And to answer the underlying question that you did you ask: yes, you have to comply with any specific FLOSS licensing requirements for this piece of JavaScript code, mainly attribution and code redistribution if the license requires it.
And to continue answering more unasked underlying questions, if the JS code is minified and the license requires corresponding source code redistribution, you would also need to make the un-minified version of that code available for redistribution. Think of minified JS much in the same way as a compiled binary.
For reference, you can check this post about a BSD-licensed JavaScript used without proper attribution in a web page and a detailed technical analysis of the case.
As an aside, this create some interesting and funny challenges when it comes to licensing requirements... Say you use a GPL-licensed bit of JavaScript code that is 100 lines and about 1KB of code.
You would technically need to include the text of the GPL to be in full compliance which may be ~ 40KB... or 40 times bigger than the code itself.
Now practically, the GPL text would need to be available but it does not have to be available inside the JavaScript or the pages embedding that JS: it can be provided separately much the same way that a GNU Bash executable does not contain the GPL text but only a reference to it and the text is provided separately.