reverse/reverse

(no submodules)

Purpose

Provides getMimeExtension for reverse lookup: given a MIME type string, returns the canonical file extension associated with that type. This is the inverse of extension-based detection — useful for generating filenames, setting Content-Disposition headers, and file download naming.

Features

Returns the canonical (first) extension for any registered MIME type
Returns undefined for unknown MIME types (no throws)
Case-insensitive MIME type matching (delegates to registry)
Returns extensions without a leading dot
O(1) lookup via the registry's forward map

Usage: Basic Example

import { getMimeExtension } from "@suaveplan/mime/reverse/reverse";

console.log(getMimeExtension("image/png"));         // "png"
console.log(getMimeExtension("application/pdf"));   // "pdf"
console.log(getMimeExtension("text/javascript"));   // "js"
console.log(getMimeExtension("unknown/type"));      // undefined

Usage: Advanced Example

import { getMimeExtension } from "@suaveplan/mime/reverse/reverse";

function buildFilename(baseName: string, mimeType: string): string {
    const ext = getMimeExtension(mimeType);
    if (!ext) return baseName; // Unknown type — keep original name
    // Avoid double extension
    return baseName.endsWith(`.${ext}`) ? baseName : `${baseName}.${ext}`;
}

// Content-Disposition header generation
function contentDisposition(mimeType: string, name: string): string {
    const ext = getMimeExtension(mimeType);
    const filename = ext ? `${name}.${ext}` : name;
    return `attachment; filename="${filename}"`;
}

console.log(contentDisposition("application/pdf", "report"));
// 'attachment; filename="report.pdf"'

API Reference

`getMimeExtension(mime: string): string | undefined`

Parameter	Type	Description
`mime`	`string`	MIME type string (e.g., `"image/png"`).

Returns: The canonical file extension string without a leading dot, or undefined if the MIME type is not in the database.

Throws: Never.

Implementation Notes

The "canonical" extension is the first element of the extensions array in the MimeEntry. The built-in database places the most common extension first by convention (e.g., "jpeg" before "jpg" for image/jpeg). Callers that need all extensions for a type should use getEntryByMime directly from @suaveplan/mime/db/registry and access entry.extensions.

Lookup Tables

The reverse index maps MIME string → preferred extension, MIME string → alias list, and alias → canonical MIME. Tables are precomputed at module load from the same curated IANA database the forward lookup uses, so the two directions can never drift. Lookups are O(1) against frozen Map instances with zero runtime cost after first import.

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