Forgive me for parroting the thoughts of those smarter than me, but there was an engaging debate on Lambda the Ultimate recently on how terrible JS is as an assembly language: http://lambda-the-ultimate.org/node/4308#comment-66084
He couldn't just have used scheme wholesale though, since a major part of JS is the integration with the DOM. He would have needed to create some custom object system anyway to support that. So it would have been a new language anyway, and due to the time constraints at the time, it would probably have had the same amount of bugs and mistakes that JS ended up with.
Subtle chains of cause and effect were at play among people involved, going back years to Silicon Graphics (Netscape drew from UIUC and SGI, plus montulli from Kansas, and jwz). Also going back through the living history of programming languages. SICP and some of the Sussman & Steele "Lambda the ..." papers made a big impression on me years before, although I did not understand their full meaning then.
Remember, I was recruited to "do Scheme", which felt like bait and switch in light of the Java deal brewing by the time I joined Netscape. My interest in languages such as Self informed a subversive agenda re: the dumbed down mission to make "Java's kid brother", to have objects without classes. Likewise with first-class functions, which were inspired by Scheme but quite different in JS, especially JS 1.0.
Apart from the "look like Java" mandate, and "object-based" as a talking point, I had little direction. Only a couple of top people at Netscape and Sun really grokked the benefit of a dynamic language for tying together components, but they were top people (marca, Rick Schell [VP Eng Netscape], Bill Joy).
Rather than dumb luck, I think a more meaningful interpretation is that I was a piece of an evolving system, exploring one particular path in a damn hurry. That system contains people playing crucial parts. Academic, business, and personal philosophical and friendship agendas all transmitted an analogue of genes: ideas and concrete inventions from functional programming and Smalltalk-related languages.
You might think "it's still luck, it could have been Forth, or TCL". Not likely. There were not years or even months to spare. I had hacked language implementations for fun since I was an undergrad, and for SGI's packet sniffing tools earlier my career. I was a C/Unix fanboy, I knew the C grammar by heart. Independent of me, the "Make it look like Java" order was not just lucky, it was congruent as a consequent, even predictable, given the rise of C in the '80s and C++ in the '90s, and the direct influence of C++ on Java.
My point is simple: the likelihood of any other language syntax than C (C++ -> Java, but really: C) was low. The likelihood of something without "objects" was also low. Netscape recruited me in part because I could hack quickly, and in part because I had some language implementation chops (not enough, in hindsight). I was "that guy", not in any brag-worthy sense, just the only person who was in the position to do the deed, with (barely) enough skills to pull it off.
Many hackers could have done a better job with more time, or perhaps a better job had they been in my shoes. Who knows? But no one at Netscape could have, and the opportunity was there and then.
The path dependence part is spot on. Netscape's business plan for 1.0 was getting out in six months or someone else would kill Mosaic and take over. The entire platform push in 1.1 (plugins) and 2 (frames, JS) was about getting on first. We knew Microsoft was coming, because Netscape had rejected a low-ball offer from them in late '94.
Still, some pretty sizable element of luck is there indeed.
If the common browser language had been brainfuck we would have had to use that.
That said, it is important to note why brainfuck (or any other blub) wasn't the common browser language (or CBL from here on in) - the CBL is the CBL because it was relatively easy for humans to write small snippets of code in it. Without that, the language would never become the CBL.
Unfortunately that statement also means that the odds were against the CBL being anything other than an imperative style language. That we got something so close to a functional language is really quite a bonus (even if I do end up having to modify strings and eval() because we aren't using s-exprs)
Note that VBScript were much more familiar to many developers, because VB was one of the most popular language at the time. But it fell by the wayside because it was not supported at ubiquitously as JS. (It was also a much worse language than JS, but that was not the reason it failed.)