URL: /rules/perf/js-file-size

---
title: "JavaScript File Size Too Large"
description: "Checks for JavaScript files that exceed recommended size limits"
---

Checks for JavaScript files that exceed recommended size limits

| | |
|---|---|
| **Rule ID** | `perf/js-file-size` |
| **Category** | [Performance](/rules/perf) |
| **Scope** | Site-wide |
| **Severity** | error |
| **Weight** | 7/10 |

## Solution

Large JavaScript files block the main thread and delay interactivity. Code-split bundles into smaller chunks, tree-shake unused exports, lazy-load non-critical scripts, and defer or async load third-party scripts. Use dynamic imports for route-based splitting.

## Options

This rule supports the following configuration options:

| Option | Type | Default | Description |
|--------|------|---------|-------------|
| `warn_bytes` | number | `256000` (250KB) | Byte size to trigger warning |
| `error_bytes` | number | `1048576` (1MB) | Byte size to trigger error |

### Configuration Example

```toml squirrel.toml
[rules."perf/js-file-size"]
warn_bytes = 256000
error_bytes = 1048576
```

## Enable / Disable

### Disable this rule

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

### Disable all Performance rules

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

### Enable only this rule

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