chore: replace eslint with biome

.github/workflows/ci.yml

@@ -12,10 +12,10 @@ jobs:
   test:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
-      - uses: actions/setup-node@v1
+      - uses: actions/checkout@v7
+      - uses: actions/setup-node@v7
         with:
-          node-version: 14
+          node-version: 24
       - name: Setup and build
         run: |
           npm ci

.github/workflows/publish-npm.yml

@@ -8,10 +8,10 @@ jobs:
   publish-npm:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
-      - uses: actions/setup-node@v1
+      - uses: actions/checkout@v7
+      - uses: actions/setup-node@v7
         with:
-          node-version: 14
+          node-version: 24
           registry-url: https://registry.npmjs.org/
       - name: Setup and build
         run: |

README.md

@@ -5,3 +5,17 @@ Chart.js test utils package. For usage examples, take a look at these repositori
 - [Chart.js](https://github.com/chartjs/Chart.js)
 - [chartjs-plugin-annotation](https://github.com/chartjs/chartjs-plugin-annotation)
 - [chartjs-plugin-datalabels](https://github.com/chartjs/chartjs-plugin-datalabels)
+
+## Development
+
+Linting and formatting are done by [Biome](https://biomejs.dev/), configured in
+`biome.jsonc`:
+
+```sh
+npm run lint     # check formatting and lint rules
+npm run format   # apply the safe fixes
+```
+
+The formatter settings mirror the `eslint-config-chartjs` style rules it
+replaced, so the formatter agrees with the existing sources rather than
+restyling them.

biome.jsonc

@@ -0,0 +1,87 @@
+{
+  "$schema": "https://biomejs.dev/schemas/2.5.13/schema.json",
+  // Biome replaces eslint, eslint-config-chartjs and eslint-plugin-es here.
+  // The formatter settings below are the eslint-config-chartjs style rules
+  // (2-space indent, single quotes, semicolons, no spacing inside braces),
+  // so that adopting the formatter is not also a restyling of the sources.
+  "files": {
+    "includes": ["**/*.js", "**/*.json", "**/*.jsonc", "!dist", "!package-lock.json"]
+  },
+  "formatter": {
+    "enabled": true,
+    "indentStyle": "space",
+    "indentWidth": 2,
+    // eslint had `max-len` off; this only wraps what is already very long.
+    "lineWidth": 120
+  },
+  "javascript": {
+    "formatter": {
+      "arrowParentheses": "always",
+      // object-curly-spacing: never
+      "bracketSpacing": false,
+      // quotes: single, avoidEscape
+      "quoteStyle": "single",
+      // semi: always
+      "semicolons": "always",
+      // comma-dangle: only-multiline -- never adding one keeps the diff small
+      "trailingCommas": "none"
+    }
+  },
+  "json": {
+    "formatter": {
+      "trailingCommas": "none"
+    }
+  },
+  "linter": {
+    "enabled": true,
+    "rules": {
+      "recommended": true,
+      "complexity": {
+        // eslint: complexity [2, 10]. Cognitive complexity is a different
+        // measure, so the threshold is not the same number.
+        "noExcessiveCognitiveComplexity": {
+          "level": "warn",
+          "options": { "maxAllowedComplexity": 15 }
+        },
+        // The sources are written in the ES5 style Karma-era Chart.js used:
+        // `var`, `function () {}` callbacks, `arguments`, string concatenation.
+        // Modernizing them is a code change, not a tooling change, so these
+        // stay off until someone makes it deliberately.
+        "noArguments": "off",
+        "useArrowFunction": "off",
+        "useDateNow": "off",
+        "useOptionalChain": "off"
+      },
+      "correctness": {
+        // Same reason: this reports `var` declared inside a block.
+        "noInnerDeclarations": "off"
+      },
+      "style": {
+        // eslint: curly [2, all]
+        "useBlockStatements": "error",
+        "useTemplate": "off"
+      },
+      "suspicious": {
+        // eslint: no-console [2, {allow: [warn, error]}]
+        "noConsole": {
+          "level": "error",
+          "options": { "allow": ["warn", "error"] }
+        },
+        // `isNaN` and `Number.isNaN` do not answer the same question: the
+        // global coerces, and the matchers rely on that.
+        "noGlobalIsFinite": "off",
+        "noGlobalIsNan": "off",
+        // The code already uses the safe `Object.prototype.hasOwnProperty.call`
+        // form; the rule only wants the newer `Object.hasOwn`.
+        "noPrototypeBuiltins": "off"
+      }
+    }
+  },
+  "assist": {
+    "actions": {
+      "source": {
+        "organizeImports": "on"
+      }
+    }
+  }
+}