Unoptimized destructuring compilation

TypeScript Version: 2.0

Code

// source ts code
let i = 1000;
while (i--) {
  let [a, b, c] = [1, 2, 3];
}

Expected behavior:

// compiled by babel
var i = 1000;
while (i--) {
  var a = 1;
  var b = 2;
  var c = 3;
}

Actual behavior:

// compiled by tsc
var i = 1000;
while (i--) {
    var _a = [1, 2, 3], a = _a[0], b = _a[1], c = _a[2];
}

On each iteration tsc creates new unnecessary array _a.

[aluanhaddad]

I like how the output always matches the syntax being transformed, it is nicely predictable. Also, if this were added, I would want to disable it during development. I would only enable it when creating a production build because there is likely to be a performance penalty for these kinds of heuristic optimizations during transpilation. It may be small, but I would want to disable it.

Unfortunately, just the notion of toggleable optimizations would introduce a lot of additional, and in my mind unnecessary complexity into the language. I real don’t like the idea of having TS dev and TS prod modes as these are in the domain of other tools.

You could argue that I am being hyperbolic by even hinting at this but I can imagine the issues requesting potential optimization x, or y, which breaks z that would crop up overnight.

[RyanCavanaugh]

Idly curious why you’re writing the intializers this way? Why not just var a = 1, b = 2, c = 3 ?