add eslint

.eslintrc.js

@@ -0,0 +1,9 @@
+module.exports = {
+  parser: '@typescript-eslint/parser',
+  parserOptions: {
+    ecmaVersion: 2020,
+    sourceType: 'module',
+  },
+  extends: ['plugin:@typescript-eslint/recommended', 'prettier/@typescript-eslint', 'plugin:prettier/recommended'],
+  rules: {},
+};

.prettierrc.js

@@ -0,0 +1,7 @@
+module.exports = {
+  semi: true,
+  trailingComma: 'all',
+  singleQuote: true,
+  printWidth: 120,
+  tabWidth: 2,
+};

functions/deep-equal.js

@@ -1,11 +1,11 @@
-"use strict";
+'use strict';
 
-module.exports = (actual, {expected}) => {
+module.exports = (actual, { expected }) => {
   if (JSON.stringify(actual) !== JSON.stringify(expected)) {
     return [
       {
         message: `${JSON.stringify(actual)} must equal ${JSON.stringify(expected)}.`,
       },
     ];
   }
-};
+};

functions/my-own-equal-func.js

@@ -1,4 +1,4 @@
-"use strict";
+'use strict';
 
 module.exports = (targetVal, opts) => {
   const { value } = opts;
@@ -9,4 +9,4 @@ module.exports = (targetVal, opts) => {
       },
     ];
   }
-};
+};

jest.config.js

@@ -1,8 +1,8 @@
 module.exports = {
-    roots: ['<rootDir>/tests'],
-    transform: {
-        '^.+\\.ts$': 'ts-jest',
-    },
-    testRegex: '^.+\\.test\\.ts$',
-    moduleFileExtensions: ['ts','js'],
-};
+  roots: ['<rootDir>/tests'],
+  transform: {
+    '^.+\\.ts$': 'ts-jest',
+  },
+  testRegex: '^.+\\.test\\.ts$',
+  moduleFileExtensions: ['ts', 'js'],
+};