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 +1,54 @@
+type Replacer = (key: string, value: any) => void;
+
+interface Options {
+	/**
+	 * Indentation as a string or number of spaces. Pass in null for no formatting.
+	 */
+	indent?: string | number | null;
+	/**
+	 * Detect indentation automatically if the file exists.
+	 */
+	detectIndent?: boolean;
+	/**
+	 * Sort the keys recursively. Optionally pass in a compare function.
+	 */
+	sortKeys?: boolean | ((a: string, b: string) => number);
+	/**
+	 * Passed into JSON.stringify.
+	 */
+	replacer?: Replacer | Array<number | string>;
+	/**
+	 * Mode used when writing the file.
+	 */
+	mode?: number;
+}
+
+/**
+ * Stringify and write JSON to a file atomically.
+ *
+ * Creates directories for you as needed.
+ *
+ * @returns {void}
+ * @example
+ * import * as writeJsonFile from 'write-json-file';
+ *
+ * writeJsonFile.sync('foo.json', {foo: true});
+ * console.log('done');
+ */
+export function sync(filepath: string, data: any, options?: Options): void;
+
+/**
+ * Stringify and write JSON to a file atomically.
+ *
+ * Creates directories for you as needed.
+ *
+ * @returns {Promise<void>}
+ * @example
+ * import writeJsonFile from 'write-json-file';
+ *
+ * (async () => {
+ * 		await writeJsonFile('foo.json', {foo: true});
+ *  	console.log('done');
+ * })();
+ */
+export default function writeJsonFile(filepath: string, data: any, options?: Options): Promise<void>;

index.js

@@ -44,7 +44,7 @@ const main = (fp, data, opts) => {
 };
 
 const mainSync = (fp, data, opts) => {
-	let indent = opts.indent;
+	let {indent} = opts;
 
 	if (opts.detectIndent) {
 		try {
@@ -62,11 +62,13 @@ 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"
+		]
+	}
 }