svelte-fast-check

0.4.5 verified Fri May 01 auth: no javascript

svelte-fast-check is a fast type and Svelte compiler warning checker for Svelte/SvelteKit projects, leveraging the TypeScript 7 (tsgo) preview (Go-based, parallel) for up to 24x faster incremental checks compared to svelte-check. Version 0.4.5 (Jan 2025) adds Windows support and fixes Node.js glob compatibility. Requires Node.js 22+ or Bun, Svelte 5+, and TypeScript 5+. Key differentiators: uses tsgo for faster incremental type checking, supports Svelte compiler warnings (unused CSS, a11y), reads warningFilter from svelte.config.js. Not included: CSS language service diagnostics.

Common errors

error SyntaxError: Import named 'glob' not found in module 'fs/promises' ↓

cause Node.js 22/24 may not expose experimental `fs.glob` in some environments; used in v0.3.0-v0.4.3

fix

Update to svelte-fast-check v0.4.4+ or use Node.js 22 with --experimental-modules flag.

error Error: Cannot find module 'svelte-fast-check' ↓

cause Package not installed or running from wrong directory when using CLI symlinks

fix

Install as devDependency: npm install -D svelte-fast-check. Ensure symlink paths are absolute (upgrade to v0.4.3+).

error TypeError: svelte.config.js warningFilter is not a function ↓

cause warningFilter must be a function; may be misconfigured in svelte.config.js

fix

Ensure warningFilter is a function that returns a boolean. Example: warningFilter: (warning) => warning.code !== 'css-unused-selector'

error error TS2322: Type 'Snippet' is not assignable to type... ↓

cause False positive from tsgo for Snippet type; known issue tsgo#1682

fix

Upgrade to v0.2.1+ which filters this false positive. Or ignore with // @ts-expect-error.

Warnings

breaking Node.js version requirement changed from >=18 to >=22 in v0.3.0 ↓

fix Upgrade Node.js to 22+ or use Bun.

gotcha CLI scripts have `#!/usr/bin/env node` shebang; `bun svelte-fast-check` runs with Node.js by default ↓

fix Use `bun --bun svelte-fast-check` to force Bun runtime, or configure in package.json.

deprecated Node.js experimental `fs.glob` used in v0.3.0 was replaced in v0.4.4 due to `SyntaxError: Import named 'glob' not found in module 'fs/promises'` ↓

fix Upgrade to v0.4.4+ which uses `tinyglobby`.

gotcha Symbolic links to CLI may fail if relative paths are used; resolved in v0.4.3 ↓

fix Upgrade to v0.4.3+ or use absolute symlinks.

gotcha TypeScript 7 (tsgo) preview is experimental; not all TypeScript features may work ↓

fix Check tsgo issue tracker for known limitations. Pin tsgo version via package.json resolutions if needed.

gotcha CSS language service diagnostics are NOT included; only TypeScript errors and Svelte compiler warnings ↓

fix Use eslint-plugin-svelte or Biome for CSS diagnostics.

gotcha Svelte compiler warnings are filtered by default using `warningFilter` from svelte.config.js; can be disabled with `--no-svelte-warnings` ↓

fix To see all warnings, use `--no-svelte-warnings false` or remove warningFilter.

Install

npm install svelte-fast-check

yarn add svelte-fast-check

pnpm add svelte-fast-check

Imports

svelteFastCheck (default export from config)
wrong
```
import { svelteFastCheck } from 'svelte-fast-check';
```
correct
```
import svelteFastCheck from 'svelte-fast-check';
```
The default export is a function for programmatic usage, not the config type.

FastCheckConfig

wrong

import { FastCheckConfig } from 'svelte-fast-check';

correct

import type { FastCheckConfig } from 'svelte-fast-check';

Use import type for TypeScript only; not a runtime value.

run (if exposed)

wrong

const run = require('svelte-fast-check');

correct

import { run } from 'svelte-fast-check';

ESM-only; requires Node.js 22+ or Bun.

MappedDiagnostic

import type { MappedDiagnostic } from 'svelte-fast-check';

Type import for diagnostics; added in v0.4.0.

Quickstart

Installs and runs svelte-fast-check with incremental mode for up to 24x faster checks.

# Install
npm install -D svelte-fast-check

# Basic usage
npx svelte-fast-check --incremental

# Or with Bun for faster runtime
bun add -D svelte-fast-check
bun --bun svelte-fast-check --incremental

# For a monorepo, specify tsconfig path:
npx svelte-fast-check --project packages/web/tsconfig.json