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Incorrect destructuring compilation of `for (let [[x] = [1]] = [];;) {...}` #9963

gkz opened this issue May 10, 2019 · 1 comment


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commented May 10, 2019

Bug Report

Current Behavior
x is not defined in the correct scope after transformation, and is not available in the for-loop body. Running the below code results in ReferenceError: x is not defined

Input Code

let i = 0;
for (let [[x] = [1]] = []; i < 1; i++) {

Current compilation:

var i = 0;

for (function () {
  var _ref = [],
      _ref$ = _ref[0];
  _ref$ = _ref$ === void 0 ? [1] : _ref$;

  var _ref$2 = _slicedToArray(_ref$, 1),
      x = _ref$2[0]; // x is defined within this IIFE, so is not available below
}(); i < 1; i++) {

Expected behavior/code
x is defined so that it is available in the body of the for-loop. If we are to run the code, we should print 1.

Babel Configuration (.babelrc, package.json, cli command)/Enviroment

  • Whatever is the latest on the Babel repl (see link above)

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commented May 10, 2019

Hey @gkz! We really appreciate you taking the time to report an issue. The collaborators
on this project attempt to help as many people as possible, but we're a limited number of volunteers,
so it's possible this won't be addressed swiftly.

If you need any help, or just have general Babel or JavaScript questions, we have a vibrant Slack
that typically always has someone willing to help. You can sign-up here
for an invite.

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