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fix(@angular-devkit/build-angular): downlevel class properties when t…
…argeting Safari <=v15 The Angular compiler is dependent on static fields being attached to user-defined classes. e.g. `static ecmp = defineComponent`. These static fields sometimes rely on variables from outside of the class. e.g. the Angular compiler generates constants for content projection that are then accessed in the static field initializer. Surprisingly such access to these variables may break in Safari <=v15 when a page is loaded without devtools open. The bug (already solved in v16 of Safari)- is very subtle, hard to re-reproduce but basically variable scope tracking is broken. This bug is triggered by additional parenthesis in the initializer expression. See: https://bugs.webkit.org/show_bug.cgi?id=236843. The TypeScript compiler may generate such additional parenthesis when it tries to adjust the `this` context when invoking methods, such as for defining animations in the `ecmp` definition. More details can be found here: #24355 (comment) To ensure Angular applications are not subject to this bug when targeting Safari <=v15. v15 Safari, both for iOS and Mac is still part of the default CLI browserslist with `last 2 Safari majors` (at time of writing). Note that it is important that the Babel plugin properly handles the downleveling of static block-defined members. TypeScript will transform static fields, like `static ecmp` into `static { this.ecmp = X }` when `useDefineForClassFields = false` (which is the case for CLI apps). The class properties plugin from Babel seems to handle this in an acceptable way. Unlike actual static fields, Babel will not use helpers like `defineProperty` for such extracted static blocks though. e.g. See repro: https://gist.github.com/devversion/dec0dea26e348c509921bf62079b60be ```js class Test { x = true; static b = true; static { this.a = true; } } // into class X { constructor() { _defineProperty(this, "x", true); } } _defineProperty(X, "b", true); X.a = true; ``` note that in practice TypeScript with `useDefineForClassFields = false` will put non-static members into the constructor as normal assignments regardless- so there would be no change by the Babel plugin. Fixes #24355.
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