What is eslint-plugin-baseline-js

Overview

eslint-plugin-baseline-js rethinks compatibility checks (e.g. compared to eslint-plugin-compat) from the Baseline perspective.

• Goal: a "Baseline" take on compat — evaluate JS/CSS/HTML with the same threshold
• Threshold: set available to 'widely' | 'newly' | YYYY
• One rule: baseline-js/use-baseline (unified message, low noise)
• Surfaces: see Scope & Terms (JS Syntax / JS Builtins / Web APIs)

Single source of truth (data‑driven)

• Primary dataset: web‑features (led by Web Platform DX)
  • GitHub: https://github.com/web-platform-dx/web-features

High‑precision detection (TypeScript)

• Beyond vanilla AST scans, we use @typescript-eslint/parser parserServices and the TypeChecker to resolve the receiver’s actual type before reporting. This lets us distinguish real platform methods from user‑defined look‑alikes.
  • Array by copy (feature: array-by-copy)
    • Verify a.toReversed() / a.toSorted() are truly Array/TypedArray methods. Same‑named methods on user classes won’t trigger.
  • Intl.Locale (feature: intl-locale-info)
    • For new Intl.Locale('ja'), only report .maximize() / .minimize() when the receiver is actually Locale.
  • Iterator methods (feature: iterator-methods)
    • Report only when the receiver is an Iterator type (union/inheritance supported).
  • Uint8Array base64/hex (feature: uint8array-base64-hex)
    • Check both static/instance paths (Uint8Array.fromBase64, u8.toBase64()) and confirm the type is Uint8Array.
• It also works through generics and aliases, e.g.: function f<T extends Array<number>>(x: T) { x.toReversed() } — we traverse the apparent type and base types to make the right call.