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-wasm provides built-in support for Deno compiled binaries through two helper functions:

initializeForDenoCompile() - Automatic initialization with offline support
prepareWasmForEmbedding() - Copies WASM file for embedding

Method 1: Simple CDN Loading (Recommended)

The simplest approach that leverages WebAssembly streaming compilation:

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

// Works in both development and compiled binaries
const taglib = await TagLib.initialize({
  wasmUrl: "https://cdn.jsdelivr.net/npm/taglib-wasm@latest/dist/taglib.wasm",
});

// Use the library
const file = await taglib.open("audio.mp3");
console.log(file.tag().title);
file.dispose();

Compile command:

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

Pros:

✅ Simple implementation
✅ Uses WebAssembly streaming compilation for optimal performance
✅ Always gets latest WASM optimizations
✅ Small binary size

Cons:

❌ Requires internet connection on first run

Method 2: Automatic Offline Support

Use the built-in helper functions for seamless offline support:

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

async function main() {
  // Automatically handles offline/online scenarios
  const taglib = await initializeForDenoCompile();

  // Process files
  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.wasm");

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

Step 2: Compile with embedded WASM

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

Step 3: Run offline

./myapp audio.mp3

How It Works

The initializeForDenoCompile() function:

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

Method 3: 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 {
      // Try to load embedded WASM
      const wasmPath = new URL("./taglib.wasm", import.meta.url);
      const wasmBinary = await Deno.readFile(wasmPath);
      return await TagLib.initialize({ wasmBinary });
    } catch (error) {
      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, writeTags } 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 writeTags(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.wasm myapp.ts

3. Path Resolution

Use URL constructor for relative paths:

const wasmPath = new URL("./taglib.wasm", import.meta.url);

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

Use TypeScript: Leverage type safety for better development experience
Handle Errors: Always wrap initialization in try-catch blocks
Provide Feedback: Show loading status to users
Test Both Modes: Ensure your app works in both development and compiled modes
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.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