Add TypeScript definition

.travis.yml

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

index.d.ts

@@ -0,0 +1,41 @@
+/// <reference types="node"/>
+
+declare const terminalImage: {
+	/**
+	Display images in the terminal.
+
+	@param imageBuffer - Buffer with the image.
+	@returns The ansi escape codes to display the image.
+
+	@example
+	```
+	import terminalImage = require('terminal-image');
+	import got = require('got');
+
+	(async () => {
+		const {body} = await got('sindresorhus.com/unicorn', {encoding: null});
+		console.log(await terminalImage.buffer(body));
+	})();
+	```
+	*/
+	buffer(imageBuffer: Buffer): Promise<string>;
+
+	/**
+	Display images in the terminal.
+
+	@param filePath - File path to the image.
+	@returns The ansi escape codes to display the image.
+
+	@example
+	```
+	import terminalImage = require('terminal-image');
+
+	(async () => {
+		console.log(await terminalImage.file('unicorn.jpg'));
+	})();
+	```
+	*/
+	file(filePath: string): Promise<string>;
+}
+
+export = terminalImage;

index.js

@@ -17,23 +17,23 @@ async function render(buffer) {
 		image.scaleToFit(columns, rows * 2);
 	}
 
-	let ret = '';
+	let result = '';
 	for (let y = 0; y < image.bitmap.height - 1; y += 2) {
 		for (let x = 0; x < image.bitmap.width; x++) {
 			const {r, g, b, a} = Jimp.intToRGBA(image.getPixelColor(x, y));
 			const {r: r2, g: g2, b: b2} = Jimp.intToRGBA(image.getPixelColor(x, y + 1));
 
 			if (a === 0) {
-				ret += chalk.reset(' ');
+				result += chalk.reset(' ');
 			} else {
-				ret += chalk.bgRgb(r, g, b).rgb(r2, g2, b2)(PIXEL);
+				result += chalk.bgRgb(r, g, b).rgb(r2, g2, b2)(PIXEL);
 			}
 		}
 
-		ret += '\n';
+		result += '\n';
 	}
 
-	return ret;
+	return result;
 }
 
 exports.buffer = async buffer => {

index.test-d.ts

@@ -0,0 +1,5 @@
+import {expectType} from 'tsd';
+import terminalImage = require('.');
+
+expectType<Promise<string>>(terminalImage.file('unicorn.jpg'));
+expectType<Promise<string>>(terminalImage.buffer(Buffer.alloc(1)));

package.json

@@ -13,10 +13,11 @@
 		"node": ">=8"
 	},
 	"scripts": {
-		"test": "xo && ava"
+		"test": "xo && ava && tsd"
 	},
 	"files": [
-		"index.js"
+		"index.js",
+		"index.d.ts"
 	],
 	"keywords": [
 		"terminal",
@@ -40,11 +41,13 @@
 	],
 	"dependencies": {
 		"@sindresorhus/jimp": "^0.3.0",
-		"chalk": "^2.4.1",
-		"term-img": "^3.0.0"
+		"chalk": "^2.4.2",
+		"term-img": "^4.1.0"
 	},
 	"devDependencies": {
-		"ava": "^0.25.0",
-		"xo": "^0.23.0"
+		"@types/node": "^11.13.8",
+		"ava": "^1.4.1",
+		"tsd": "^0.7.2",
+		"xo": "^0.24.0"
 	}
 }