Using TagLib-Wasm with Deno Compile

This comprehensive guide explains how to use TagLib-Wasm in compiled Deno binaries, with multiple approaches for different use cases.

Overview

TagLib.initialize() auto-detects Deno compile mode. When running inside a compiled binary, it automatically switches to Emscripten buffer mode and attempts to load embedded Wasm — no special API needed.

For advanced use cases, explicit helpers are also available:

• initializeForDenoCompile() - Explicit initialization with custom Wasm path
• prepareWasmForEmbedding() - Copies WASM file for embedding

Method 1: Auto-Detection (Recommended)

TagLib.initialize() transparently handles compiled binaries:

import { TagLib } from "@charlesw/taglib-wasm";

// Works in development, Deno compile, browsers — everywhere
const taglib = await TagLib.initialize();

using file = await taglib.open("audio.mp3");
console.log(file.tag().title);

For offline support, embed the Wasm file at compile time:

# Prepare WASM file
deno run --allow-read --allow-write -e \
  "import { prepareWasmForEmbedding } from '@charlesw/taglib-wasm'; await prepareWasmForEmbedding();"

# Compile with embedded WASM
deno compile --allow-read --include taglib-web.wasm myapp.ts

How it works:

1. Detects compiled binary via Deno.mainModule containing deno-compile://
2. Automatically sets forceBufferMode: true (Emscripten, not WASI)
3. Tries to load embedded Wasm using the multi-strategy fallback (see Path Resolution)
4. Warns and falls back gracefully if embedded Wasm not found

Method 2: CDN Loading

For online-only tools, use a CDN URL:

import { TagLib } from "@charlesw/taglib-wasm";

const taglib = await TagLib.initialize({
  wasmUrl: "https://cdn.jsdelivr.net/npm/taglib-wasm@latest/dist/taglib.wasm",
});

using file = await taglib.open("audio.mp3");
console.log(file.tag().title);

Compile command:

deno compile --allow-read --allow-net myapp.ts

Pros:

• Small binary size
• Always gets latest WASM optimizations

Cons:

• Requires internet connection on first run

Method 3: Explicit Helper (Custom Wasm Path)

Use initializeForDenoCompile() when you need a custom embedded Wasm path:

import { initializeForDenoCompile } from "@charlesw/taglib-wasm";
import { readTags } from "@charlesw/taglib-wasm/simple";

async function main() {
  // Custom embedded path
  const taglib = await initializeForDenoCompile("./assets/taglib-web.wasm");

  for (const filePath of Deno.args) {
    const tags = await readTags(filePath);
    console.log(`${filePath}:`, tags);
  }
}

if (import.meta.main) {
  await main();
}

Build Process

Step 1: Prepare WASM file (run once during build)

// prepare-offline.ts
import { prepareWasmForEmbedding } from "@charlesw/taglib-wasm";

await prepareWasmForEmbedding("./taglib-web.wasm");

deno run --allow-read --allow-write prepare-offline.ts

Step 2: Compile with embedded WASM

deno compile --allow-read --include taglib-web.wasm myapp.ts

Step 3: Run offline

./myapp audio.mp3

How It Works

The initializeForDenoCompile() function:

1. Detects if running as compiled binary using Deno.mainModule
2. Attempts to load embedded WASM from ./taglib-web.wasm
3. Falls back to network fetch if not found (for development)

Method 4: Manual Control (Advanced)

For full control over the loading strategy:

import { TagLib } from "@charlesw/taglib-wasm";

async function initializeTagLib(): Promise<TagLib> {
  // Detect if running as compiled binary
  const isCompiled = Deno.mainModule.includes("deno-compile://");

  if (isCompiled) {
    // Try multiple resolution strategies
    const strategies = [
      () => Deno.readFile(new URL("./taglib-web.wasm", Deno.mainModule)),
      () => Deno.readFile(new URL("./taglib-web.wasm", import.meta.url)),
      () => Deno.readFile("taglib-web.wasm"),
    ];
    for (const strategy of strategies) {
      try {
        const wasmBinary = await strategy();
        return await TagLib.initialize({ wasmBinary });
      } catch {
        // Try next strategy
      }
    }
    console.warn("Embedded WASM not found, falling back to CDN");
  }

  // Development or fallback
  return await TagLib.initialize({
    wasmUrl: "https://cdn.jsdelivr.net/npm/taglib-wasm@latest/dist/taglib.wasm",
  });
}

// Usage
const taglib = await initializeTagLib();

Complete Production Example

Here's a production-ready implementation with error handling:

#!/usr/bin/env -S deno run --allow-read --allow-net

import { initializeForDenoCompile } from "@charlesw/taglib-wasm";
import { readTags, writeTagsToFile } from "@charlesw/taglib-wasm/simple";

async function processAudioFile(filePath: string) {
  try {
    // Read existing tags
    const tags = await readTags(filePath);
    console.log(`\n📄 File: ${filePath}`);
    console.log(`  Title: ${tags.title || "(none)"}`);
    console.log(`  Artist: ${tags.artist || "(none)"}`);
    console.log(`  Album: ${tags.album || "(none)"}`);

    // Modify tags if needed
    if (!tags.comment?.includes("Processed")) {
      await writeTagsToFile(filePath, {
        ...tags,
        comment: `${tags.comment || ""} - Processed by TagLib-Wasm`,
      });
      console.log("  ✅ Updated comment tag");
    }
  } catch (error) {
    console.error(`  ❌ Error: ${error.message}`);
  }
}

async function main() {
  if (Deno.args.length === 0) {
    console.log("Usage: audio-processor <files...>");
    console.log("Example: audio-processor *.mp3");
    Deno.exit(1);
  }

  console.log("🎵 Audio Metadata Processor");
  console.log("Initializing TagLib-Wasm...");

  try {
    // Initialize with automatic offline support
    const taglib = await initializeForDenoCompile();
    console.log("✅ Ready to process files\n");

    // Process all files
    for (const filePath of Deno.args) {
      await processAudioFile(filePath);
    }

    console.log("\n✅ All files processed!");
  } catch (error) {
    console.error("Fatal error:", error.message);
    Deno.exit(1);
  }
}

if (import.meta.main) {
  await main();
}

Key Implementation Details

1. Detection of Compiled Binaries

const isCompiled = Deno.mainModule.includes("deno-compile://");

2. Embedding WASM Files

Use the --include flag when compiling:

deno compile --allow-read --include taglib-web.wasm myapp.ts

3. Path Resolution

Embedded Wasm is resolved using a multi-strategy fallback:

1. Deno.mainModule — relative to the user's entry point (where --include embeds files)
2. import.meta.url — relative to the library module (fallback)
3. Bare path — virtual root / CWD

This ensures the Wasm file is found regardless of whether the compiled binary resolves paths relative to the entry point or the library module.

4. Environment Configuration

Support runtime configuration:

const WASM_URL = Deno.env.get("TAGLIB_WASM_URL") ||
  "https://cdn.jsdelivr.net/npm/taglib-wasm@latest/dist/taglib.wasm";

Comparison Table

Method	Offline Support	Binary Size	Implementation Complexity	Best For
CDN Loading	❌	Small	Simple	Online tools, web services
Auto Embedding	✅	+500KB	Medium	CLI tools, offline apps
Manual Control	✅	+500KB	Complex	Custom requirements

Best Practices

1. Use TypeScript: Leverage type safety for better development experience
2. Handle Errors: Always wrap initialization in try-catch blocks
3. Provide Feedback: Show loading status to users
4. Test Both Modes: Ensure your app works in both development and compiled modes
5. Document Dependencies: Make it clear if your tool requires internet access

Common Issues and Solutions

Issue: "Module not found" in compiled binary

Solution: Ensure you used --include taglib-web.wasm when compiling

Issue: Large binary size

Solution: Use CDN loading if offline support isn't required

Issue: Slow initialization

Solution: Use CDN with streaming compilation for faster startup

Issue: Network errors

Solution: Implement retry logic or provide offline fallback

Example Projects

Complete working examples are available in the repository:

• examples/deno-compile/simple-app.ts - CDN loading example
• examples/deno-compile/app.ts - Advanced embedding example
• examples/deno/offline-compile.ts - Using helper functions

Tips for Production

• Cache WASM locally: For frequently used tools, cache the WASM file locally
• Use your own CDN: Host the WASM file on your infrastructure for reliability
• Version pinning: Use specific versions instead of @latest for stability
• Progress indicators: Show download progress when fetching from CDN
• Graceful degradation: Provide meaningful error messages when initialization fails