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Normative: End this TDZ before running initializers
#92
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Previously, the TDZ of `this` in a subclass constructor ended when
the `super()` call was entirely finished. However, `this` is visible
as not being in TDZ running initializers. For example:
{
let f;
class A extends (class {}) {
x = (this, f());
constructor() { f = () => this; super(); }
};
new A;
}
Previously, `f()` would lead to a ReferenceError in this case, while
`this` would evaluate to the new instance under construction.
This patch tweaks the TDZ to end a little bit sooner, so that `this`
is defined inside of the constructor's scope *before* the initializers
are run. In the above example, there would be no ReferenceError
under the semantics in this patch.
Thanks to Caitlin Potter, Kevin Gibbons and Jordan Harband for
contributing to the discussion that led to this change.
bakkot
approved these changes
Apr 6, 2018
|
lgtm |
|
Wow, what a quick review! Thanks. Would anyone be interested in writing test262 tests for this change? |
|
@littledan Sure, give me a minute. |
|
lgtm |
|
Tests merged tc39/test262#1507 I'm going to spend a little more time with the tests and these changes to verify coverage. |
kisg
pushed a commit
to paul99/v8mips
that referenced
this pull request
Apr 17, 2018
Class fields needs to be initialized after `this` is bound, as per the new spec change: tc39/proposal-class-fields#92 This CL moves the initialization of `this` from parser desugaring to the bytecode generator. Bug: v8:7647 Change-Id: I20f749403e5a4d2f06a39726cf39012ceb541987 Reviewed-on: https://chromium-review.googlesource.com/1014383 Reviewed-by: Mythri Alle <[email protected]> Commit-Queue: Sathya Gunasekaran <[email protected]> Cr-Commit-Position: refs/heads/master@{#52646}
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Previously, the TDZ of
thisin a subclass constructor ended whenthe
super()call was entirely finished. However,thisis visibleas not being in TDZ running initializers. For example:
Previously,
f()would lead to a ReferenceError in this case, whilethiswould evaluate to the new instance under construction.This patch tweaks the TDZ to end a little bit sooner, so that
thisis defined inside of the constructor's scope before the initializers
are run. In the above example, there would be no ReferenceError
under the semantics in this patch.
Thanks to Caitlin Potter, Kevin Gibbons and Jordan Harband for
contributing to the discussion that led to this change.