Upgrade to Eslint 9

Gruntfile.js

@@ -1,5 +1,8 @@
 // Gruntfile for music21j
 // Copyright Michael Scott Asato Cuthbert (michael.asato.cuthbert@gmail.com), BSD License
+
+// this system is in the process of being phased out in 2025 but is not there yet.
+
 const path = require('path');
 const webpack = require('webpack');
 const ESLintPlugin = require('eslint-webpack-plugin');
@@ -66,7 +69,7 @@ module.exports = grunt => {
                 presets: babel_presets,
                 plugins: [
                     '@babel/plugin-transform-object-assign',
-                    '@babel/plugin-proposal-export-namespace-from',
+                    '@babel/plugin-transform-export-namespace-from',
                     '@babel/plugin-proposal-class-properties',
                 ],
             },
@@ -201,9 +204,6 @@ module.exports = grunt => {
         },
         eslint: {
             target: SOURCES.concat(TEST_SOURCES),
-            options: {
-                overrideConfigFile: '.eslintrc.json',
-            },
         },
         qunit: {
             files: ['tests/gruntTest.html'],

eslint.config.js

@@ -0,0 +1,144 @@
+// keeping this as a commonJS file for now -- PyCharm goes crazy if we make it a .mjs file -- thinks
+// everything ending in js is then one.
+const globals = require('globals');
+const { configs: airbnb } = require('eslint-config-airbnb-extended/legacy');
+const eslint_parser = require('@typescript-eslint/parser');
+const eslint_plugin = require('@typescript-eslint/eslint-plugin');
+
+const no_unused_vars_config = [
+    'warn',
+    {
+        args: 'none',
+        caughtErrors: 'none',
+        varsIgnorePattern: '^_.*|^i$|^j$|^unused|^junk|^counter',
+    },
+];
+
+
+module.exports = [
+    ...airbnb.base.recommended,  // this is the flat-eslint version of airbnb-base
+    {
+        ignores: ['releases/*', 'build/*', 'node_modules/*'],
+        files: ['**/*.js', '**/*.ts'],   // tsx would go here, etc.
+        languageOptions: {
+            ecmaVersion: 'latest',
+            globals: {
+                ...globals.browser,
+                ...globals.jquery,
+                ...globals.es2026,  // this should be the latest in globals, not what we transpile to.
+            },
+        },
+        rules: {
+            'array-bracket-spacing': ['off'],
+            'arrow-body-style': ['off'],
+            'arrow-parens': ['off'],
+            'brace-style': ['off'],
+            'camelcase': ['off'],
+            'class-methods-use-this': ['off'],
+            'comma-dangle': ['warn', {
+                arrays: 'only-multiline',
+                objects: 'always-multiline',
+                imports: 'always-multiline',
+                exports: 'always-multiline',
+                functions: 'ignore',
+            }],
+            'curly': ['warn', 'all'],
+            'dot-location': ['warn', 'property'],
+            'dot-notation': ['error'],
+            'function-paren-newline': ['warn', 'consistent'],
+            'indent': ['warn', 4, {
+                ignoredNodes: ['TemplateLiteral *'],
+            }],
+            'import/extensions': ['off'],
+            'import/prefer-default-export': ['off'],
+            'import/no-named-as-default': ['off'],
+            'import/no-named-as-default-member': ['off'],
+            'import/no-unresolved': ['off'],
+            'import/no-extraneous-dependencies': ['off'],
+            'linebreak-style': ['off'],
+            'lines-between-class-members': ['warn', 'always', {
+                exceptAfterSingleLine: true,
+            }],
+            'max-classes-per-file': ['off'],
+            'max-len': [
+                'warn', {
+                    code: 120,
+                    ignoreUrls: true,
+                    ignoreTemplateLiterals: true,
+                    ignoreTrailingComments: true,
+                },
+            ],
+            'new-cap': ['off'],
+            'no-case-declarations': ['error'],
+            'no-console': ['off'],
+            'no-continue': ['off'],
+            'no-confusing-arrow': ['off'],
+            'no-else-return': ['off'],
+            'no-floating-decimal': ['warn'],
+            'no-lonely-if': ['off'],
+            'no-mixed-operators': ['off'],
+            'no-multi-spaces': ['off'],
+            'no-multiple-empty-lines': ['warn', { max: 3 }],
+            'no-param-reassign': ['off'],
+            'no-plusplus': ['error', { allowForLoopAfterthoughts: true }],
+            'no-promise-executor-return': ['off'],
+            'no-restricted-syntax': [
+                2,
+                'DebuggerStatement',
+                'LabeledStatement',
+                'WithStatement',
+            ],
+            'no-return-assign': ['warn', 'except-parens'],
+            'no-shadow': ['off'],
+            'no-trailing-spaces': ['off'],
+            'no-use-before-define': ['off'],
+            'no-underscore-dangle': ['off'],
+            'no-unused-vars': no_unused_vars_config,
+            'no-useless-return': ['warn'],
+            'object-curly-spacing': ['off'],
+            'object-curly-newline': ['warn', {
+                ObjectExpression: { multiline: true, minProperties: 5, consistent: true },
+                ObjectPattern: { multiline: true, minProperties: 5, consistent: true },
+                ImportDeclaration: { multiline: true, minProperties: 5, consistent: true },
+                ExportDeclaration: { multiline: true, minProperties: 5, consistent: true },
+            }],
+            'object-property-newline': ['off'],
+            'object-shorthand': ['off'],
+            'operator-linebreak': ['off'],
+            'padded-blocks': ['off'],
+            'prefer-const': [
+                'warn',
+                {
+                    'destructuring': 'all',
+                }
+            ],
+            'prefer-destructuring': ['off'],
+            'prefer-object-spread': ['warn'],
+            'prefer-regex-literals': ['off'],
+            'prefer-template': ['off'],
+            'quote-props': ['off'],
+            'quotes': ['warn'],
+            'radix': ['off'],
+            'semi-style': ['warn'],
+            'space-infix-ops': ['off'],
+            'spaced-comment': ['off'],
+            'strict': ['error', 'global'],
+            'yoda': ['error', 'never', { exceptRange: true }],
+        },
+    },
+    {
+        // formerly "overrides"
+        files: ['**/*.ts'],
+        plugins: {
+            '@typescript-eslint': eslint_plugin,
+        },
+        languageOptions: {
+            parser: eslint_parser,
+        },
+        rules: {
+            '@typescript-eslint/no-unused-vars': no_unused_vars_config,
+            'no-undef': 'off',
+            'no-unused-vars': 'off',
+        },
+    },
+];