Improve performance for concurrent conversions by re-using browser context

src/cli.ts

@@ -12,6 +12,7 @@ import Listr from 'listr';
 import path from 'path';
 import { PackageJson } from '.';
 import { Config, defaultConfig } from './lib/config';
+import { closeBrowser } from './lib/generate-output';
 import { help } from './lib/help';
 import { setProcessAndTermTitle } from './lib/helpers';
 import { convertMdToPdf } from './lib/md-to-pdf';
@@ -126,10 +127,11 @@ async function main(args: typeof cliFlags, config: Config) {
 
 	if (stdin) {
 		await convertMdToPdf({ content: stdin }, config, args)
-			.then(async () => closeServer(server))
-			.catch(async (error: Error) => {
+			.finally(async () => {
+				await closeBrowser();
 				await closeServer(server);
-
+			})
+			.catch((error: Error) => {
 				throw error;
 			});
 
@@ -143,7 +145,7 @@ async function main(args: typeof cliFlags, config: Config) {
 
 	await new Listr(files.map(getListrTask), { concurrent: true, exitOnError: false })
 		.run()
-		.then(() => {
+		.then(async () => {
 			if (args['--watch']) {
 				console.log(chalk.bgBlue('\n watching for changes \n'));
 
@@ -155,7 +157,8 @@ async function main(args: typeof cliFlags, config: Config) {
 					new Listr([getListrTask(file)], { exitOnError: false }).run().catch(console.error),
 				);
 			} else {
-				server.close();
+				await closeBrowser();
+				await closeServer(server);
 			}
 		})
 		.catch((error: Error) => {

src/lib/generate-output.ts

@@ -16,14 +16,28 @@ interface BasicOutput {
 	filename: string | undefined;
 }
 
+/**
+ * Store a single browser instance reference so that we can re-use it.
+ */
+let browserPromise: Promise<puppeteer.Browser> | undefined;
+
+/**
+ * Close the browser instance.
+ */
+export const closeBrowser = async () => (await browserPromise)?.close();
+
 /**
  * Generate the output (either PDF or HTML).
  */
 export async function generateOutput(html: string, relativePath: string, config: PdfConfig): Promise<PdfOutput>;
 export async function generateOutput(html: string, relativePath: string, config: HtmlConfig): Promise<HtmlOutput>;
 export async function generateOutput(html: string, relativePath: string, config: Config): Promise<Output>;
 export async function generateOutput(html: string, relativePath: string, config: Config): Promise<Output> {
-	const browser = await puppeteer.launch({ devtools: config.devtools, ...config.launch_options });
+	if (!browserPromise) {
+		browserPromise = puppeteer.launch({ devtools: config.devtools, ...config.launch_options });
+	}
+
+	const browser = await browserPromise;
 
 	const page = await browser.newPage();
 
@@ -65,7 +79,7 @@ export async function generateOutput(html: string, relativePath: string, config:
 		outputFileContent = await page.pdf(config.pdf_options);
 	}
 
-	await browser.close();
+	await page.close();
 
 	return config.devtools ? (undefined as any) : { filename: config.dest, content: outputFileContent };
 }