It looks like Babel is taking some invalid shortcuts here. The DestructuringAssignmentEvaluation runtime semantics[1] require the same source object (the parameter `value`) to be used throughout the destructuring operation. Babel compiles the first destructuring into
var bar = foo.bar; var qaz = foo.qaz; So `foo` gets looked up twice, with the second lookup resulting in a different value, the one that the `bar` getter assigned to `foo`. In SpiderMonkey, both getters get called (you can check this with console.log calls in the getters) because the destructuring operates on the same value throughout. Curiously, the inline destructuring in the console.log call at the end fares better here: it assigns `foo` to a temporary variable `_foo`, so changing the value of `foo` doesn't influence results. (I do wonder if that causes `foo` to be leaked forever, though: `_foo` is a global variable defined at the script's top.) [1] http://www.ecma-international.org/ecma-262/6.0/index.html#sec-runtime-semantics-destructuringassignmentevaluation On Mon, Jul 20, 2015 at 10:58 AM, Michał Wadas <[email protected]> wrote: > Following code: > > > var foo = { > get bar() { > foo = { > qaz: 'bar-r' > }; > return 'bar-c'; > }, > get qaz() { > foo = { > bar: 'qaz-r' > } > return 'qaz-c'; > } > }; > > let {bar, qaz} = foo; > console.log(({bar, qaz} = foo)); > > Firefox: > Object { bar: "qaz-r" } > Babel: > Object { qaz: "bar-r" } > _______________________________________________ > es-discuss mailing list > [email protected] > https://mail.mozilla.org/listinfo/es-discuss >
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