Add ESLint and Prettier (#21)

Closes #5.

.circleci/config.yml

@@ -26,6 +26,8 @@ jobs:
           paths:
             - ~/.cache/yarn
 
+      - run: yarn lint
+
       - run: yarn test
 
       - run: yarn build

.eslintrc.js

@@ -0,0 +1,139 @@
+'use strict';
+
+const restrictedGlobals = require('confusing-browser-globals');
+
+const OFF = 'off';
+const ERROR = 'error';
+
+// Files that are transformed and can use ES6/JSX.
+const esNextPaths = [
+  // Internal forwarding modules
+  './index.js',
+  // Source files
+  'src/**/*.js',
+  // Jest
+  'scripts/jest/setupTests.js',
+];
+
+// Files that we distribute on npm that should be ES5-only.
+const es5Paths = ['npm/**/*.js'];
+
+module.exports = {
+  env: {
+    browser: true,
+    es6: true,
+    node: true,
+  },
+  extends: [
+    'eslint:recommended',
+    'plugin:react/recommended',
+    'plugin:prettier/recommended',
+    'prettier/react',
+  ],
+  globals: {
+    Atomics: 'readonly',
+    SharedArrayBuffer: 'readonly',
+  },
+  parser: 'babel-eslint',
+  parserOptions: {
+    ecmaVersion: 2018,
+    sourceType: 'script',
+  },
+  plugins: ['react'],
+  settings: {
+    react: {
+      version: 'detect',
+    },
+  },
+  rules: {
+    'no-console': ERROR,
+    'no-empty': OFF,
+    'no-restricted-globals': [ERROR, ...restrictedGlobals],
+    'no-unsafe-finally': OFF,
+    'no-unused-vars': [ERROR, {args: 'none'}],
+    'no-useless-escape': OFF,
+
+    // We apply these settings to files that should run on Node.
+    // They can't use JSX or ES6 modules, and must be in strict mode.
+    // They can, however, use other ES6 features.
+    // (Note these rules are overridden later for source files.)
+    'no-var': ERROR,
+    strict: ERROR,
+  },
+  overrides: [
+    {
+      // We apply these settings to files that we ship through npm.
+      // They must be ES5.
+      files: es5Paths,
+      parser: 'espree',
+      parserOptions: {
+        ecmaVersion: 5,
+        sourceType: 'script',
+      },
+      rules: {
+        'no-var': OFF,
+        strict: ERROR,
+      },
+      overrides: [
+        {
+          // These files are ES5 but with ESM support.
+          files: ['npm/esm/**/*.js'],
+          parserOptions: {
+            // Although this is supposed to be 5, ESLint doesn't allow sourceType 'module' when ecmaVersion < 2015.
+            // See https://github.com/eslint/eslint/issues/9687#issuecomment-508448526
+            ecmaVersion: 2015,
+            sourceType: 'module',
+          },
+        },
+      ],
+    },
+    {
+      // We apply these settings to the source files that get compiled.
+      // They can use all features including JSX (but shouldn't use `var`).
+      files: esNextPaths,
+      parserOptions: {
+        ecmaVersion: 2018,
+        sourceType: 'module',
+      },
+      rules: {
+        'no-var': ERROR,
+        strict: OFF,
+      },
+    },
+    {
+      // Rollup understands ESM
+      files: ['rollup.config.js'],
+      parserOptions: {
+        ecmaVersion: 2018,
+        sourceType: 'module',
+      },
+    },
+    {
+      files: ['**/__tests__/**/*.js', 'scripts/jest/setupTests.js'],
+      env: {
+        'jest/globals': true,
+      },
+      plugins: ['jest'],
+      rules: {
+        // https://github.com/jest-community/eslint-plugin-jest
+        'jest/no-focused-tests': ERROR,
+        'jest/valid-expect': ERROR,
+        'jest/valid-expect-in-promise': ERROR,
+
+        // React & JSX
+        // This isn't useful in our test code
+        'react/display-name': OFF,
+        'react/jsx-key': OFF,
+        'react/no-deprecated': OFF,
+        'react/no-string-refs': OFF,
+        'react/prop-types': OFF,
+      },
+    },
+    {
+      files: ['scripts/**/*.js', 'npm/**/*.js'],
+      rules: {
+        'no-console': OFF,
+      },
+    },
+  ],
+};

.gitignore

@@ -1,2 +1,3 @@
 node_modules
 build/
+.eslintcache

babel.config.js

@@ -1,3 +1,5 @@
+'use strict';
+
 module.exports = {
   presets: [
     [

jest.config.js

@@ -1,3 +1,5 @@
+'use strict';
+
 module.exports = {
   modulePathIgnorePatterns: ['<rootDir>/build/'],
   setupFilesAfterEnv: ['./scripts/jest/setupTests.js'],

package.json

@@ -21,21 +21,31 @@
   },
   "devDependencies": {
     "@babel/cli": "^7.8.4",
-    "@babel/core": "^7.8.4",
+    "@babel/core": "^7.8.6",
     "@babel/plugin-proposal-class-properties": "^7.8.3",
     "@babel/plugin-proposal-object-rest-spread": "^7.8.3",
-    "@babel/plugin-transform-classes": "^7.8.3",
+    "@babel/plugin-transform-classes": "^7.8.6",
     "@babel/plugin-transform-react-jsx-source": "^7.8.3",
     "@babel/plugin-transform-template-literals": "^7.8.3",
-    "@babel/preset-env": "^7.8.4",
+    "@babel/preset-env": "^7.8.6",
     "@babel/preset-react": "^7.8.3",
     "@rollup/plugin-commonjs": "^11.0.1",
     "@rollup/plugin-node-resolve": "^7.0.0",
     "@rollup/plugin-replace": "^2.3.0",
+    "babel-eslint": "^10.1.0",
     "babel-jest": "^25.1.0",
+    "confusing-browser-globals": "^1.0.9",
+    "eslint": "^6.8.0",
+    "eslint-config-prettier": "^6.10.0",
+    "eslint-plugin-jest": "^23.8.0",
+    "eslint-plugin-prettier": "^3.1.2",
+    "eslint-plugin-react": "^7.18.3",
     "fs-extra": "^8.1.0",
+    "husky": "^4.2.3",
     "jest": "^25.1.0",
     "jest-diff": "^25.1.0",
+    "lint-staged": "^10.0.8",
+    "prettier": "1.19.1",
     "react": "^16.12.0",
     "rimraf": "^3.0.1",
     "rollup": "^1.30.1",
@@ -57,7 +67,16 @@
     "prebuild": "rimraf build",
     "build": "rollup --config",
     "postbuild": "node ./scripts/copyFiles.js",
+    "lint": "eslint --ignore-path .gitignore .",
     "test": "jest",
     "test:debug": "node --inspect-brk node_modules/jest/bin/jest.js --runInBand --no-cache"
+  },
+  "husky": {
+    "hooks": {
+      "pre-commit": "lint-staged"
+    }
+  },
+  "lint-staged": {
+    "*.js": "eslint --cache --fix"
   }
 }

src/ReactShallowRenderer.js

@@ -596,7 +596,7 @@ See https://fb.me/react-invalid-hook-call for tips about how to debug and fix th
       if (process.env.NODE_ENV !== 'production') {
         ReactDebugCurrentFrame.getCurrentStack = prevGetStack;
       }
-   }
+    }
 
     this._rendering = false;
     this._updater._invokeCallbacks();

src/shared/ReactSharedInternals.js

@@ -10,15 +10,17 @@ import React from 'react';
 const ReactSharedInternals =
   React.__SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED;
 
+const hasOwnProperty = Object.prototype.hasOwnProperty;
+
 // Prevent newer renderers from RTE when used with older react package versions.
 // Current owner and dispatcher used to share the same ref,
 // but PR #14548 split them out to better support the react-debug-tools package.
-if (!ReactSharedInternals.hasOwnProperty('ReactCurrentDispatcher')) {
+if (!hasOwnProperty.call(ReactSharedInternals, 'ReactCurrentDispatcher')) {
   ReactSharedInternals.ReactCurrentDispatcher = {
     current: null,
   };
 }
-if (!ReactSharedInternals.hasOwnProperty('ReactCurrentBatchConfig')) {
+if (!hasOwnProperty.call(ReactSharedInternals, 'ReactCurrentBatchConfig')) {
   ReactSharedInternals.ReactCurrentBatchConfig = {
     suspense: null,
   };

src/shared/consoleWithStackDev.js

@@ -41,6 +41,7 @@ function printWarning(level, format, args) {
     argsWithFormat.unshift('Warning: ' + format);
     // We intentionally don't use spread (or .apply) directly because it
     // breaks IE9: https://github.com/facebook/react/issues/13610
+    // eslint-disable-next-line no-console
     Function.prototype.apply.call(console[level], console, argsWithFormat);
 
     try {