• Version: v8.8.1
• Platform: Darwin sprite.local 17.0.0 Darwin Kernel Version 17.0.0: Thu Aug 24 21:48:19 PDT 2017; root:xnu-4570.1.46~2/RELEASE_X86_64 x86_64
• Subsystem: _tls_wrap.js

Documentation for the ALPNProtocols option (found here) indicates that an array of strings should be acceptable:

\\ Broken
var socket = new tls.TLSSocket(null, { ALPNProtocols: ['http/1.1'] });

However, the example above produces this error:

TypeError: Must give a Buffer as first argument
    at TLSSocket._init (_tls_wrap.js:516:9)
    at new TLSSocket (_tls_wrap.js:304:8)
    at repl:1:14
    at ContextifyScript.Script.runInThisContext (vm.js:50:33)
    at REPLServer.defaultEval (repl.js:240:29)
    at bound (domain.js:301:14)
    at REPLServer.runBound [as eval] (domain.js:314:12)
    at REPLServer.onLine (repl.js:441:10)
    at emitOne (events.js:120:20)
    at REPLServer.emit (events.js:210:7)

From which I inferred that I had to use a buffer:

\\ Working
var buffer = Buffer.from([8, ...Buffer.from('http/1.1')]);
var socket = new tls.TLSSocket(null, { ALPNProtocols: buffer });

If this is indeed a documentation bug, I'd be happy to open a pull request. I'll take a shot at a code bug if the issue is determined to be there instead.