Object initializer creates unused variable

[SamuelMarks]

#1082 called for [Object initializer](the https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Object_initializer) ES6 syntax.

Using tsc/typescript 1.7.5 with Node 5.3.0.

Input:

const x = {['c']: 'b'};

Output [tsc input.ts]:

var x = (_a = {}, _a['c'] = 'b', _a);
var _a;

[RyanCavanaugh]

I'm confused by which variable you think is unused? _a is used as a temporary during object initialization and cannot be removed. What do you expect the emit to be?

[SamuelMarks]

What's with line 2?

[RyanCavanaugh]

Again, what do you expect the emit to be?

[SamuelMarks]

Either the _a being declared before its use, or not declared with var at all.

[DanielRosenwasser]

var declarations are hoisted. We take advantage of this at emit-time and aggregate all temporaries we determine we need as we build up the output. Then, at the end of an appropriate scope, we emit the declaration for all temporaries. There's nothing wrong with this semantically, and the variables are not unused.