I recently finished Resilient Web Design by Jeremy Keith, a book my friend Charles Roper recommended. In Chapter 4: Languages, Jeremy shares a website called Everyone has JavaScript, right?
The user requests your web app. Has the page loaded yet? Did the HTTP request for the JavaScript succeed? Did the HTTP request for the JavaScript complete? Does the corporate firewall block JavaScript? Does their ISP or mobile operator interfere with downloaded JavaScript? Have they switched off JavaScript? Do they have add‐ons or plug‐ins installed which inject script or alter the DOM in ways you didn’t anticipate? Is the Content Delivery Network up? Does their browser support the JavaScript you’ve written?
All of this challenges the ridiculous notion that "JavaScript is only unavailable when the user has deliberately disabled it".
That's rarely the case.