Rename variables for clarity and update browser pool management

browserPool.js

@@ -58,17 +58,21 @@ async function renderHtml(html, waitTime = 1000) {
             height: VIEWPORT_HEIGHT
         });
 
-        await page.setContent(html, { waitUntil: 'networkidle0' });
+        await page.setContent(html, { waitUntil: ['load', 'domcontentloaded', 'networkidle0'] });
+
+        // wait for body to be ready
+        await page.waitForSelector('body');
 
         // wait for any animations or laoding
         await new Promise(resolve => setTimeout(resolve, waitTime));
 
         const screenshot = await page.screenshot({
             type: 'png',
-            fullPage: false
+            fullPage: false,
+            encoding: 'binary'
         });
 
-        return screenshot;
+        return Buffer.from(screenshot);
     } finally {
         if (page) await page.close();
         releaseBrowser(browser);