Support tagged templates in ES5 and ES3

[Alxandr]

Tagged templates are fairly easy to implement using ES5 and ES3, you simply turn the following:

fn`Hello ${you}! You're looking ${adjective} today!`

into the following:

fn(["Hello ", "! You're looking ", " today!"], you, adjective);

(sample taken from http://updates.html5rocks.com/2015/01/ES6-Template-Strings)

[ivogabe]

That has already been implemented in #1589. Note that the first argument of the downlevel call should have a raw property. We ended up with the following code:

(_a = ["Hello ", "! You're looking ", " today!"], _a.raw = ["Hello ", "! You're looking ", " today!"], fn(_a, you, adjective));
var _a;

[Alxandr]

Oh, damn, github search by default only searched open issues :-/.

Babel does more or less the same thing, except it uses a generated helper (and also does some Object.freeze if the browser supports it). I just tested this on the playground on the typescriptlang website, but I guess it hasn't been released yet.

[filipstachura]

Incoming in 1.5 :)

[Alxandr]

Great. Thanks. Sorry for duplicate issue :).

[DanielRosenwasser]

No worries - as a note, we thought about Object.freeze but I guess we were leaning towards the extremes of either doing it as correctly as possible (with making a cache of template strings arrays) or as cleanly as possible with ES3 compat (the way it is currently slated for 1.5). I think that the way @ivogabe did it is clean, canonical, and understandable.

Just for documentation, the duplicate issue is #1590.