unicode.json

{ "inline":
  { "unicode-support-in-js-today":"💩"
  , "unicode-support-in-js-someday":"😁" }
, "surrogates":
  { "unicode-support-in-js-today":"\uf09f\u92a9"
  , "unicode-support-in-js-someday":"\uf09f\u9881" }
}

use-unicode.js

function assert(x) {
  if (!x) console.error("assertion failed")
  else console.error("assertion passed")
}

{ "use unicode" // opt-in so we don't break the web

  var x = "\u1F638" // > 2 byte unicode code point
  var y = "😁" // face with open mouth and smiling eyes

  assert(x.length === 1) // less important, but ideal
  assert(y.length === 1) // less important, but ideal
  assert(x === y) // unicode code points should match literals
  console.log(x) // <-- should output a smiley, not "ὣ8"
  console.log(y) // <-- should output a smiley, not mochibake
  assert(JSON.stringify(y) === JSON.stringify(x))
  assert(JSON.parse(JSON.stringify(y)) === y)
  assert(JSON.parse(JSON.stringify(x)) === x)

  assert(x.indexOf(y) === 0)
  assert(y.indexOf(x) === 0)
  var arr = ["a", "b", "c"]
  var axbxc = arr.join(x)
  var aybyc = arr.join(y)
  assert(axbxc.split(x)[1] === arr[1])
  assert(axbxc.split(y)[1] === arr[1])
  // etc.
  // They're just characters, and just strings.
  // No special anything, just treat it like any other character.  
}

It appears that, in node at least, we're being bitten by http://code.google.com/p/v8/issues/detail?id=761. We will work with v8 to figure out the best solution there, to get from utf8 bytes into a JavaScript string, which doesn't arbitrarily trash non-BMP characters. I apologize for misunderstanding the issue and impugning the good name of JavaScript. (In my defense, it's a particularly complicated issue, and JavaScript's name isn't really all that good ;)

Nevertheless, I think that clearly the long-term correct fix is for JavaScript to handle unicode intelligently (albeit with the presence of big red switches), so I'm very happy to see your proposal.