[eslint] add eslint

.eslintrc

@@ -0,0 +1,20 @@
+{
+    "root": true,
+
+    "extends": "@ljharb",
+
+    "rules": {
+        "consistent-return": 1,
+        "indent": [2, 4],
+        "sort-keys": 0,
+    },
+
+    "overrides": [
+        {
+            "files": "example/**",
+            "rules": {
+                "no-console": 0,
+            },
+        },
+    ],
+}

example/defined.js

@@ -1,4 +1,6 @@
+'use strict';
+
 var defined = require('../');
-var opts = { y : false, w : 4 };
+var opts = { y: false, w: 4 };
 var x = defined(opts.x, opts.y, opts.w, 8);
 console.log(x);

index.js

@@ -1,5 +1,9 @@
-module.exports = function () {
+'use strict';
+
+module.exports = function defined() {
     for (var i = 0; i < arguments.length; i++) {
-        if (arguments[i] !== undefined) return arguments[i];
+        if (typeof arguments[i] !== 'undefined') {
+            return arguments[i];
+        }
     }
 };

package.json

@@ -8,10 +8,14 @@
         "test": "test"
     },
     "devDependencies": {
+        "@ljharb/eslint-config": "^21.0.0",
         "aud": "^2.0.1",
+        "eslint": "=8.8.0",
         "tape": "^5.6.1"
     },
     "scripts": {
+        "lint": "eslint --ext=js,mjs .",
+        "pretest": "npm run lint",
         "tests-only": "tape 'test/**/*.js'",
         "test": "npm run tests-only",
         "posttest": "aud --production"

test/def.js

@@ -1,22 +1,24 @@
+'use strict';
+
 var defined = require('../');
 var test = require('tape');
 
 test('defined-or', function (t) {
-    var u = undefined;
-    
+    var u = void undefined;
+
     t.equal(defined(), u, 'empty arguments');
     t.equal(defined(u), u, '1 undefined');
     t.equal(defined(u, u), u, '2 undefined');
     t.equal(defined(u, u, u, u), u, '4 undefineds');
-    
+
     t.equal(defined(undefined, false, true), false, 'false[0]');
     t.equal(defined(false, true), false, 'false[1]');
     t.equal(defined(undefined, 0, true), 0, 'zero[0]');
     t.equal(defined(0, true), 0, 'zero[1]');
-    
+
     t.equal(defined(3, undefined, 4), 3, 'first arg');
     t.equal(defined(undefined, 3, 4), 3, 'second arg');
     t.equal(defined(undefined, undefined, 3), 3, 'third arg');
-    
+
     t.end();
 });

test/falsy.js

@@ -1,9 +1,11 @@
+'use strict';
+
 var test = require('tape');
 var defined = require('../');
 
 test('falsy', function (t) {
     t.plan(1);
-    var opts = { y : false, w : 4 };
+    var opts = { y: false, w: 4 };
     var x = defined(opts.x, opts.y, opts.w, 8);
     t.equal(x, false);
 });