URL: /rules/perf/duplicate-js

---
title: "Duplicate JavaScript"
description: "Detects duplicate JavaScript libraries loaded multiple times"
---

Detects duplicate JavaScript libraries loaded multiple times

| | |
|---|---|
| **Rule ID** | `perf/duplicate-js` |
| **Category** | [Performance](/rules/perf) |
| **Scope** | Per-page |
| **Severity** | warning |
| **Weight** | 5/10 |

## Solution

Remove duplicate JavaScript library loads to reduce page weight and avoid conflicts. Check for the same library loaded from different CDNs or versions. Use a single source for each dependency. Consider using a module bundler to deduplicate shared dependencies.

## Enable / Disable

### Disable this rule

```toml squirrel.toml
[rules]
disable = ["perf/duplicate-js"]
```

### Disable all Performance rules

```toml squirrel.toml
[rules]
disable = ["perf/*"]
```

### Enable only this rule

```toml squirrel.toml
[rules]
enable = ["perf/duplicate-js"]
disable = ["*"]
```