---
title: "Use Async Loading for JavaScript Modules to Prevent Render Blocking | bseoa"
description: "A JavaScript module on your page is loading synchronously, which can block the rendering of your page. Modern JavaScript modules should be loaded asynchronousl…"
image: "https://www.blackseoanalyzer.com/static/images/black-seo-analyzer-og-image.png"
canonical: "https://www.blackseoanalyzer.com/en/technical-seo/performance-analyzer/module-needs-async"
language: "en"
---

# Use Async Loading for JavaScript Modules to Prevent Render Blocking

Performance Analyzer

## What is this warning?

A JavaScript module on your page is loading synchronously, which can block the rendering of your page. Modern JavaScript modules should be loaded asynchronously to prevent them from delaying the display of content to users.

## How to Fix This Issue

### How to Fix It

#### The Problem

```
<script type="module" src="/js/app.js"></script>
```

#### The Solution

Add the `async` attribute to module scripts to prevent them from blocking page rendering.

```
<script type="module" src="/js/app.js" async></script>
```

#### Why This Works

Async loading allows the browser to continue parsing and rendering the page while the module downloads and executes, leading to faster perceived performance and better Core Web Vitals scores.

### SEO Impact

This issue can affect your site's search engine rankings and user experience. Addressing it promptly helps ensure optimal performance and visibility in search results.

### Automatic Detection

bseoa automatically checks for this warning during site analysis, along with hundreds of other technical SEO issues.

## Other Performance Analyzer issues

- [Add width and height Attributes to Images to Prevent Layout Shift](https://www.blackseoanalyzer.com/en/technical-seo/performance-analyzer/image-dimensions)
- [Add Cache-Control Headers to Improve Browser Caching](https://www.blackseoanalyzer.com/en/technical-seo/performance-analyzer/missing-cache-control-header)
- [Add Crossorigin Attribute to Font Preloads for Better Performance](https://www.blackseoanalyzer.com/en/technical-seo/performance-analyzer/font-crossorigin)
- [Add Media Attributes to Stylesheets for Conditional Loading](https://www.blackseoanalyzer.com/en/technical-seo/performance-analyzer/stylesheet-media-attribute)
- [Add Preload Hints for Critical Resources to Improve Loading Performance](https://www.blackseoanalyzer.com/en/technical-seo/performance-analyzer/missing-preload-hint)
- [Add Preload Hints for Important Scripts to Improve Loading Performance](https://www.blackseoanalyzer.com/en/technical-seo/performance-analyzer/script-preload-hint)
- [Eliminate Render-Blocking JavaScript to Speed Up Page Load](https://www.blackseoanalyzer.com/en/technical-seo/performance-analyzer/render-blocking-script)
- [Enable Text Compression to Reduce File Sizes](https://www.blackseoanalyzer.com/en/technical-seo/performance-analyzer/resource-not-compressed)
- [font-display: swap Explained: Stop Invisible Text While Fonts Load](https://www.blackseoanalyzer.com/en/technical-seo/performance-analyzer/font-font-display)
- [Implement Cache Busting for Static Resources to Ensure Updates](https://www.blackseoanalyzer.com/en/technical-seo/performance-analyzer/missing-cache-busting)
- [Implement Responsive Images for All Device Sizes](https://www.blackseoanalyzer.com/en/technical-seo/performance-analyzer/responsive-image)
- [Increase Browser Cache Times for Static Assets](https://www.blackseoanalyzer.com/en/technical-seo/performance-analyzer/insufficient-cache-time)
- [Load Print Stylesheets Asynchronously to Improve Performance](https://www.blackseoanalyzer.com/en/technical-seo/performance-analyzer/print-stylesheet-loading)
- [Optimize Critical Rendering Path for Faster Page Display](https://www.blackseoanalyzer.com/en/technical-seo/performance-analyzer/long-critical-path)
- [Preload Critical CSS for Faster Page Rendering](https://www.blackseoanalyzer.com/en/technical-seo/performance-analyzer/critical-css-preload)
- [Preload Critical Scripts for Faster Interactivity](https://www.blackseoanalyzer.com/en/technical-seo/performance-analyzer/critical-script-preload)
- [Reduce Size of Critical Resources for Faster Page Loading](https://www.blackseoanalyzer.com/en/technical-seo/performance-analyzer/large-critical-resource)
- [Serve Images in Modern Formats like WebP for Faster Loading](https://www.blackseoanalyzer.com/en/technical-seo/performance-analyzer/image-not-optimized)
- [Use preconnect to Speed Up Connections to Third-Party Domains](https://www.blackseoanalyzer.com/en/technical-seo/performance-analyzer/missing-preconnect-hint)
- [Use Efficient Font Formats for Better Web Performance](https://www.blackseoanalyzer.com/en/technical-seo/performance-analyzer/font-format)
- [Use Lazy Loading for Off-Screen Images to Improve Performance](https://www.blackseoanalyzer.com/en/technical-seo/performance-analyzer/lazy-load-image)
- [Use the Modern WOFF2 Font Format for Better Compression](https://www.blackseoanalyzer.com/en/technical-seo/performance-analyzer/font-not-woff2)

## Ready to Unlock Your Site's Full SEO Potential?

Choose the license that fits your needs and start getting the deep, actionable insights you deserve.

[Download Free Trial](https://www.blackseoanalyzer.com/en/free-trial) [Purchase Single License](https://www.blackseoanalyzer.com/buy/single)

```json
{"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://www.blackseoanalyzer.com/#organization","name":"Fiscus Technology, LLC","url":"https://www.blackseoanalyzer.com/","logo":"https://www.blackseoanalyzer.com/static/images/black-seo-analyzer.png","founder":{"@type":"Person","name":"Seth Black"}},{"@type":"WebSite","@id":"https://www.blackseoanalyzer.com/#website","name":"bseoa","url":"https://www.blackseoanalyzer.com/","publisher":{"@id":"https://www.blackseoanalyzer.com/#organization"}},{"@type":"TechArticle","@id":"https://www.blackseoanalyzer.com/en/technical-seo/performance-analyzer/module-needs-async#article","headline":"Use Async Loading for JavaScript Modules to Prevent Render Blocking","name":"Use Async Loading for JavaScript Modules to Prevent Render Blocking","description":"A JavaScript module on your page is loading synchronously, which can block the rendering of your page. Modern JavaScript modules should be loaded asynchronously to prevent them from delaying the display of content to users.","url":"https://www.blackseoanalyzer.com/en/technical-seo/performance-analyzer/module-needs-async","image":{"@type":"ImageObject","url":"https://www.blackseoanalyzer.com/static/images/black-seo-analyzer-og-image.png","width":1200,"height":630},"author":{"@type":"Person","name":"Seth Black","url":"https://www.blackseoanalyzer.com/about"},"publisher":{"@id":"https://www.blackseoanalyzer.com/#organization"},"mainEntityOfPage":{"@type":"WebPage","@id":"https://www.blackseoanalyzer.com/en/technical-seo/performance-analyzer/module-needs-async"},"inLanguage":"en-US","keywords":"technical SEO, SEO warning, Seth Black&#39;s SEO Analyzer"},{"@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://www.blackseoanalyzer.com/"},{"@type":"ListItem","position":2,"name":"Technical SEO Warnings","item":"https://www.blackseoanalyzer.com/en/technical-seo"},{"@type":"ListItem","position":3,"name":"Use Async Loading for JavaScript Modules to Prevent Render Blocking","item":"https://www.blackseoanalyzer.com/en/technical-seo/performance-analyzer/module-needs-async"}]}]}
```