feat: add eslint config and ignore files

.eslintignore

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+node_modules/

.eslintrc.json

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+{
+  "env": {
+    "node": true,
+    "es2021": true,
+    "jest": true
+  },
+  "extends": "eslint:recommended",
+  "parserOptions": {
+    "ecmaVersion": "latest"
+  },
+  "rules": {}
+}

.gitignore

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+node_modules/

.husky/pre-commit

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+npx lint-staged

index.js

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+function sum(a, b) {
+       return a + b;
+     }
+     module.exports = sum;

index.test.js

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+const sum = require('./index');
+     test('adds 1 + 2 to equal 3', () => {
+       expect(sum(1, 2)).toBe(3);
+     });

package.json

@@ -0,0 +1,25 @@
+{
+  "name": "my-ci-project",
+  "version": "1.0.0",
+  "description": "",
+  "main": "index.js",
+  "scripts": {
+    "test": "jest",
+    "lint": "eslint ."
+  },
+  "keywords": [],
+  "author": "",
+  "license": "ISC",
+  "devDependencies": {
+    "eslint": "^8.57.0",
+    "husky": "^9.0.11",
+    "jest": "^29.7.0",
+    "lint-staged": "^15.2.2"
+  },
+  "lint-staged": {
+    "*.js": [
+      "eslint --fix",
+      "jest --findRelatedTests"
+    ]
+  }
+}