---
title: "Eliminate Render-Blocking JavaScript to Speed Up Page Load | bseoa"
description: "A JavaScript file is preventing your page from displaying until it has been fully downloaded and processed. This is a major cause of slow-loading websites, as …"
image: "https://www.blackseoanalyzer.com/static/images/black-seo-analyzer-og-image.png"
canonical: "https://www.blackseoanalyzer.com/en/technical-seo/performance-analyzer/render-blocking-script"
language: "en"
---

# Eliminate Render-Blocking JavaScript to Speed Up Page Load

Performance Analyzer

## What is this warning?

A JavaScript file is preventing your page from displaying until it has been fully downloaded and processed. This is a major cause of slow-loading websites, as it leaves your visitors staring at a blank screen. Fixing this is a critical step for improving your Core Web Vitals and overall user experience.

## How to Fix This Issue

### How to Fix It

#### The Problem

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

#### The Solution

Add the `defer` attribute to the script tag. This allows the browser to continue building the page while the script downloads in the background.

```
<script src="/js/app.js" defer></script>
```

#### Why This Works

Deferring scripts ensures that they don't block the critical rendering path. This leads to a much faster First Contentful Paint (FCP), which is a key metric for user-perceived performance.

### 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)
- [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 Async Loading for JavaScript Modules to Prevent Render Blocking](https://www.blackseoanalyzer.com/en/technical-seo/performance-analyzer/module-needs-async)
- [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)

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