Array destructuring puts declaration after assignment

[sixinli]

TypeScript Version:

1.8.7

Code

let firstValue = 1;
let secondValue = 2;
[firstValue, secondValue] = [3, 4];

Expected behavior:

var firstValue = 1;
var secondValue = 2;
var _a;
_a = [3, 4], firstValue = _a[0], secondValue = _a[1];

Actual behavior:

var firstValue = 1;
var secondValue = 2;
_a = [3, 4], firstValue = _a[0], secondValue = _a[1];
var _a;

Closure Compiler reports _a as unreachable code / use before definition. While this works at runtime, it's not a good practice and looks like a bug in tsc.

[mhegazy]

duplicate of #7017

[mhegazy]

as explained in #7017 (comment), we intend to change this in the future, just to make the code more idiomatic and less machine-generated-like.