Require Node.js 8, add TypeScript definition (#6)

.gitattributes

@@ -1,2 +1 @@
-* text=auto
-*.js text eol=lf
+* text=auto eol=lf

.travis.yml

@@ -1,4 +1,5 @@
 language: node_js
 node_js:
+  - '12'
+  - '10'
   - '8'
-  - '6'

index.d.ts

@@ -0,0 +1,16 @@
+/**
+Lowercase the keys of an object.
+
+@returns A new object with the keys lowercased.
+
+@example
+```
+import lowercaseKeys = require('lowercase-keys');
+
+lowercaseKeys({FOO: true, bAr: false});
+//=> {foo: true, bar: false}
+```
+*/
+declare function lowercaseKeys<T extends unknown>(object: {[key: string]: T}): {[key: string]: T};
+
+export = lowercaseKeys;

index.js

@@ -1,10 +1,10 @@
 'use strict';
 module.exports = object => {
-	const ret = {};
+	const result = {};
 
 	for (const [key, value] of Object.entries(object)) {
-		ret[key.toLowerCase()] = value;
+		result[key.toLowerCase()] = value;
 	}
 
-	return ret;
+	return result;
 };

index.test-d.ts

@@ -0,0 +1,5 @@
+import {expectType} from 'tsd';
+import lowercaseKeys = require('.');
+
+expectType<{[key: string]: boolean}>(lowercaseKeys({FOO: true, bAr: false}));
+expectType<{[key: string]: string | number}>(lowercaseKeys({foo: 'bar', baz: 1}));

package.json

@@ -10,13 +10,14 @@
 		"url": "sindresorhus.com"
 	},
 	"engines": {
-		"node": ">=6"
+		"node": ">=8"
 	},
 	"scripts": {
-		"test": "xo && ava"
+		"test": "xo && ava && tsd"
 	},
 	"files": [
-		"index.js"
+		"index.js",
+		"index.d.ts"
 	],
 	"keywords": [
 		"object",
@@ -30,7 +31,8 @@
 		"key"
 	],
 	"devDependencies": {
-		"ava": "*",
-		"xo": "*"
+		"ava": "^1.4.1",
+		"tsd": "^0.7.2",
+		"xo": "^0.24.0"
 	}
 }

test.js

@@ -1,7 +1,7 @@
 import test from 'ava';
-import m from '.';
+import lowercaseKeys from '.';
 
 test('main', t => {
-	t.true(m({FOO: true}).foo);
-	t.true(m({FOO: true, bAr: true}).bar);
+	t.true(lowercaseKeys({FOO: true}).foo);
+	t.true(lowercaseKeys({FOO: true, bAr: true}).bar);
 });