Mime-detector NPM

mime-detector

A TypeScript module that accurately detects file MIME types by examining both file contents (magic bytes) and extensions.

Features

Accurate file type detection using magic bytes (file signatures)
Fallback to extension-based detection when magic bytes aren't conclusive
Support for common document, image, audio, and video formats
Written in TypeScript with full type definitions
Zero runtime dependencies

Installation

npm install mime-detector

Usage

import { getMimeType, getMimeExtension, isDocument, isImage, isAudio, isVideo } from 'mime-detector';

// Get MIME type
console.log(await getMimeType('https://example.com/document.pdf')); // 'application/pdf'
console.log(await getMimeType('https://example.com/image.jpg')); // 'image/jpeg'

// Get file extension from MIME type
console.log(getMimeExtension('image/jpeg')); // '.jpg'
console.log(getMimeExtension('application/pdf')); // '.pdf'

// Check file type
console.log(await isDocument('https://example.com/document.pdf')); // true
console.log(await isImage('https://example.com/image.jpg')); // true
console.log(await isAudio('https://example.com/song.mp3')); // true
console.log(await isVideo('https://example.com/movie.mp4')); // true

API

getMimeType(filePath: string): Promise

Returns the MIME type for the given file path. First attempts to detect the type by reading the file's magic bytes, then falls back to extension-based detection if necessary.

getMimeExtension(mimeType: string): string | null

Returns the corresponding file extension (including the dot) for a given MIME type. Returns null if no matching extension is found.

Helper Functions

isDocument(filePath: string): Promise<boolean> - Checks if the file is a document
isImage(filePath: string): Promise<boolean> - Checks if the file is an image
isAudio(filePath: string): Promise<boolean> - Checks if the file is an audio file
isVideo(filePath: string): Promise<boolean> - Checks if the file is a video file

Supported Formats

Documents

PDF (.pdf)
Microsoft Word (.doc, .docx)
Text (.txt)
Rich Text Format (.rtf)

Images

JPEG (.jpg, .jpeg)
PNG (.png)
GIF (.gif)
WebP (.webp)
SVG (.svg)

Audio

MP3 (.mp3)
WAV (.wav)
OGG (.ogg)
M4A (.m4a)

Video

MP4 (.mp4)
WebM (.webm)
AVI (.avi)
QuickTime (.mov)
Matroska (.mkv)

Magic Bytes Detection

The module first attempts to detect file types by examining their magic bytes (file signatures). This provides more accurate detection than extension-based methods alone, as it looks at the actual file contents. Currently supports magic bytes detection for:

PDF files
JPEG images
PNG images
GIF images
WebP images
SVG images
MP3 audio
MP4 video
WebM video

For other formats, or when magic bytes detection fails, the module falls back to extension-based detection.

Error Handling

If the file cannot be read (e.g., due to permissions or if it doesn't exist), the module falls back to extension-based detection. If the file type cannot be determined, it returns 'application/octet-stream'.