ECMAScript 2023; analyze V8 performance; Rome v12.1.0

• Change Array by copy
• Array find from last
• Symbols as WeakMap keys
• Hashbang grammar – to support (and ignore) #! syntax in JavaScript proper

It also summarizes major proposals that are in the pipeline for after ES2023.

[Quote:]

Overoptimizing infrequently used code paths wastes time and resources, so we needed tooling to help us analyze poorly performing code to find actual, tangible improvements that we could make. We built benchmarking tools to monitor compiler performance over time. We used CPU profiling and heap snapshots to investigate performance regressions. But these tools often didn’t give us the details we needed for fine tuning. So, for the past few years we’ve been working on a tool called Deopt Explorer that we’ve used internally to help us explore the various deoptimizations, inline caches, and object types that V8 produces when the compiler is executing.

[...]

Deopt Explorer is a VS Code extension that can analyze trace logs produced by V8.

• Stage 3 decorators
• Version control support. “In this release, only git is supported, and you’ll be able to ignore files and directories inside the .gitignore file.”
• More linting rules
• rome migrate: Update your configuration whenever Rome introduces breaking changes.
• New help command