00342452e2
* Fix OOB string character access in Printer#_maybeAddParen. The `_maybeAddParen` method of the `Printer` class does ```js const chaPost = str[i + 1] ``` without checking that `i + 1` is still within the bounds of `str`. It seems like this triggers fairly often that the `str[i + 1]` access is out of bounds. The first out of bounds access will turn the KeyedLoadIC (in case of V8) into *MEGAMORPHIC* state, which is significantly slower for strings (there's a fix in flight for V8 to mitigate the cost a bit in that case). Even worse than that, the out of bounds access also pollutes the later comparisons, namely ```js chaPost === "/" ``` and ```js chaPost === "*" ``` which are now no longer monomorphic on strings, since `chaPost` was sometimes `undefined`. This is a non-breaking performance fix, which improves babel execution on the [web-tooling-benchmark](github.com/v8/web-tooling-benchmark) workload by around 6-9%. * Restructure and optimize the code a bit.
The compiler for writing next generation JavaScript.
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Babel is community-driven and thus mostly maintained by a group of volunteers. It has a lot of companies and projects using it but almost no sponsors/people funded to work on it. If you'd like to help maintain the future of the project, please consider:
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Intro
Babel is a tool that helps you write code in the latest version of JavaScript. When your supported environments don't support certain features natively, Babel will help you compile those features down to a supported version.
In
// ES2015 arrow function
[1, 2, 3].map((n) => n + 1);
Out
[1, 2, 3].map(function(n) {
return n + 1;
});
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