Add TypeScript definition and require Node.js 6

.gitignore

@@ -1 +1,2 @@
 node_modules
+yarn.lock

.travis.yml

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

index.d.ts

@@ -0,0 +1,62 @@
+export type Replacer = (key: string, value: any) => void;
+export type SortKeys = (a: string, b: string) => number;
+export type JSONStringifyable = object | number | string;
+
+export interface Options {
+	/**
+	 * Indentation as a string or number of spaces. Pass in null for no formatting.
+	 *
+	 * @default '\t'
+	 */
+	indent?: string | number | null;
+	/**
+	 * Detect indentation automatically if the file exists.
+	 *
+	 * @default false
+	 */
+	detectIndent?: boolean;
+	/**
+	 * Sort the keys recursively. Optionally pass in a compare function.
+	 *
+	 * @default false
+	 */
+	sortKeys?: boolean | SortKeys;
+	/**
+	 * Passed into `JSON.stringify`.
+	 */
+	replacer?: Replacer | Array<number | string>;
+	/**
+	 * Mode used when writing the file.
+	 *
+	 * @default 0o666
+	 */
+	mode?: number;
+}
+
+/**
+ * Stringify and write JSON to a file atomically.
+ *
+ * Creates directories for you as needed.
+ *
+ * @example
+ * import * as writeJsonFile from 'write-json-file';
+ *
+ * writeJsonFile.sync('foo.json', {foo: true});
+ * console.log('done');
+ */
+export function sync(filepath: string, data: JSONStringifyable, options?: Options): void;
+
+/**
+ * Stringify and write JSON to a file atomically.
+ *
+ * Creates directories for you as needed.
+ *
+ * @example
+ * import writeJsonFile from 'write-json-file';
+ *
+ * (async () => {
+ * 	await writeJsonFile('foo.json', {foo: true});
+ * 	console.log('done');
+ * })();
+ */
+export default function writeJsonFile(filepath: string, data: JSONStringifyable, options?: Options): Promise<void>;

index.js

@@ -44,11 +44,12 @@ const main = (fp, data, opts) => {
 };
 
 const mainSync = (fp, data, opts) => {
-	let indent = opts.indent;
+	let {indent} = opts;
 
 	if (opts.detectIndent) {
 		try {
 			const file = fs.readFileSync(fp, 'utf8');
+			// eslint-disable-next-line prefer-destructuring
 			indent = detectIndent(file).indent;
 		} catch (err) {
 			if (err.code !== 'ENOENT') {
@@ -62,11 +63,13 @@ const mainSync = (fp, data, opts) => {
 	return writeFileAtomic.sync(fp, `${json}\n`, {mode: opts.mode});
 };
 
-module.exports = (fp, data, opts) => {
+const writeJsonFile = (fp, data, opts) => {
 	return makeDir(path.dirname(fp), {fs})
 		.then(() => init(main, fp, data, opts));
 };
 
+module.exports = writeJsonFile;
+module.exports.default = writeJsonFile;
 module.exports.sync = (fp, data, opts) => {
 	makeDir.sync(path.dirname(fp), {fs});
 	init(mainSync, fp, data, opts);

package.json

@@ -10,13 +10,14 @@
     "url": "sindresorhus.com"
   },
   "engines": {
-    "node": ">=4"
+    "node": ">=6"
   },
   "scripts": {
     "test": "xo && ava"
   },
   "files": [
-    "index.js"
+    "index.js",
+    "index.d.ts"
   ],
   "keywords": [
     "write",
@@ -44,5 +45,10 @@
     "ava": "*",
     "tempfile": "^2.0.0",
     "xo": "*"
+  },
+  "xo": {
+    "ignores": [
+      "index.d.ts"
+    ]
   }
 }