Add TypeScript definition

Author: kevva

index.d.ts

@@ -0,0 +1,29 @@
+/// <reference types="node"/>
+import {Metadata, PNG, PNGOptions} from 'pngjs';
+
+/**
+Parse a PNG.
+
+@param buffer - A PNG image buffer.
+@param options - See the [pngjs options](https://github.com/lukeapage/pngjs#options).
+@returns The parsed PNG image.
+
+@example
+```
+import * as fs from 'fs';
+import parsePng = require('parse-png');
+
+(async () => {
+	const png = await parsePng(fs.readFileSync('unicorn.png'));
+
+	png.adjustGamma();
+	png.pack().pipe(fs.createWriteStream('unicorn-adjusted.png'));
+})();
+```
+*/
+declare function parsePng(
+	buffer: Buffer,
+	options?: PNGOptions
+): Promise<PNG & Metadata>;
+
+export = parsePng;

index.js

@@ -1,13 +1,13 @@
 'use strict';
 const {PNG} = require('pngjs');
 
-module.exports = async (buffer, opts) => {
+module.exports = async (buffer, options) => {
 	if (!Buffer.isBuffer(buffer)) {
 		throw new TypeError(`Expected \`buffer\` to be of type \`Buffer\` but received type \`${typeof buffer}\``);
 	}
 
 	return new Promise((resolve, reject) => {
-		let png = new PNG(opts);
+		let png = new PNG(options);
 
 		png.on('metadata', data => {
 			png = Object.assign(png, data);

index.test-d.ts

@@ -0,0 +1,13 @@
+/// <reference types="node"/>
+import {expectError, expectType} from 'tsd';
+import {Metadata, PNG, PNGOptions} from 'pngjs';
+import parsePng = require('.');
+
+expectType<Promise<PNG & Metadata>>(parsePng(Buffer.from('foo')));
+expectType<Promise<PNG & Metadata>>(
+	parsePng(Buffer.from('foo'), {
+		width: 0,
+		bgColor: {red: 0, green: 0, blue: 0}
+	})
+);
+expectError(parsePng(Buffer.from('foo'), {foo: 'bar'}));

package.json

@@ -13,10 +13,11 @@
 		"node": ">=10"
 	},
 	"scripts": {
-		"test": "xo && ava"
+		"test": "xo && ava && tsd"
 	},
 	"files": [
-		"index.js"
+		"index.js",
+		"index.d.ts"
 	],
 	"keywords": [
 		"parse",
@@ -27,9 +28,12 @@
 		"pngjs": "^3.3.0"
 	},
 	"devDependencies": {
+		"@types/node": "^12.7.5",
+		"@types/pngjs": "^3.3.2",
 		"ava": "^2.4.0",
 		"file-type": "^7.2.0",
 		"get-stream": "^3.0.0",
+		"tsd": "^0.7.4",
 		"xo": "^0.24.0"
 	}
 }