JS String Builtins Proposal Could Fix WebAssembly Text Handling

If you've ever tried to build a text editor or data processor with WebAssembly, you know the pain. String handling was so bad that most people just gave up and went back to plain JavaScript. The new builtins fix the nightmare that was passing text between JS and WASM.

The Old Way Was Fucking Terrible

Before WebAssembly 3.0, JS strings came into WASM as externref objects—basically useless black boxes you couldn't actually use. You had three equally shitty options:

Copy everything into linear memory: This doubled your memory usage and required encoding/decoding every string. Our text editor was using 2GB just to process a 1GB file. Ridiculous.

Call back to JavaScript for everything: Every string operation became a slow-ass function call. You might as well not use WebAssembly at all.

Split processing between JS and WASM: Copy data back and forth constantly, making everything slower than just using JavaScript.

I spent like 2 weeks fucking around with a CSV parser, trying to get decent performance. Finally gave up and rewrote the whole thing in JS. Made WebAssembly feel like a waste of time.

What Actually Works Now

WebAssembly 3.0 adds builtin functions you can import that let you manipulate JS strings directly. No more marshaling bullshit, no more copying everything around.

You get functions to:

Read string properties: Get length, character codes, substrings without copying anything. Our syntax highlighter got way faster, went from taking forever to actually being usable.

Compare strings properly: Native comparison that works with JS strings directly instead of converting everything to byte arrays first.

Build new strings efficiently: Concatenation and substring operations that don't require going through the JS boundary.

Handle UTF-16 correctly: Direct access to JS's UTF-16 representation without the UTF-8 conversion nightmare that used to break on emoji.

How Much Faster Is It Really?

Our text processing pipeline got way faster. Haven't done any formal benchmarks because who has time for that shit, but the difference is obvious when you're not constantly copying strings around.

The wins come from:

• No malloc/free dance: String data stays in JS's optimized storage. No more allocating WASM memory just to hold text temporarily.
• No UTF-8/UTF-16 conversion hell: Remember spending hours debugging why emoji broke your parser? That's gone.
• Actual function calls instead of JS callbacks: Builtin functions are fast. Calling back to JS every time you need string length was killing performance.

The bigger your strings, the bigger the improvement. Our log processor used to choke on large files; now it doesn't die immediately.

Security That Doesn't Get in Your Way

The builtins keep WebAssembly's security model intact. You can read string data but can't corrupt JS strings—you have to explicitly create new ones through the provided functions.

This means WASM modules can't fuck up your JavaScript strings or access shit they shouldn't see. The interface is locked down but actually useful, unlike the old externref approach that was secure but useless.

JS engines can still do their optimization tricks without exposing internals to WASM. It just works without making you choose between security and performance, which is nice for once.

So the string builtins fix a ton of real problems. Instead of the academic bullshit, here's what actually got faster in apps we use every day.

Text Editors Don't Suck at Syntax Highlighting Anymore

Monaco Editor (VS Code in the browser) was painfully slow with large files because it had to copy text data into WASM memory for every syntax highlighting pass. Now it can parse JavaScript strings directly without the constant memory copying.

Our code editor used to choke on big files. Syntax highlighting would take forever and freeze the browser. With string builtins, it handles large files without dying.

Language servers like TypeScript's LSP were basically impossible to run in browsers because string analysis was so fucking slow. Now the TypeScript language server actually works in the browser instead of being completely useless.

CSV and Log Processing Actually Works

Before this, CSV parsers in the browser were a joke. Processing big CSV files meant doubling your memory usage just to copy strings into WASM. Our log analysis dashboard would crash users' browsers trying to process server logs.

Now you can parse CSV files directly from JavaScript strings without the marshaling nightmare. Our dashboard went from crashing on large files to actually working on datasets that used to kill browsers.

JSON processing got way faster too. No more copying massive JSON strings just to parse them in WASM.

Markdown and Template Engines Don't Choke

Markdown processors were another pain point. Complex markdown with syntax highlighting, math notation, or diagrams was impossibly slow because every string operation needed memory copying.

Now our documentation generator processes huge markdown files with complex extensions without timing out. Way faster than before, though I haven't timed it exactly.

Template engines like Handlebars can finally run their core logic in WASM without the performance penalty. Our static site generator was embarrassingly slow before this.

Actually Useful for Non-English Text

Right-to-left text processing, complex scripts, and locale-specific string handling was basically broken before. The marshaling overhead made international text processing unusable.

Now translation tools and spell checkers can run in WASM without the constant string copying that made them slower than just using JavaScript. Our multilingual app finally works properly for Arabic and Chinese users.

Migration That Doesn't Suck

The biggest win is you can migrate string-heavy code to WASM incrementally instead of rewriting everything. Before, it was all-or-nothing because the string handling was so painful.

We've been slowly moving our text processing libraries from JavaScript to WASM without breaking existing integrations. The string builtins make this actually feasible instead of a nightmare refactoring project.

Legacy C++ text processing libraries can finally be ported to WASM without giving up on browser integration. Our PDF processing library was stuck in JavaScript because the WASM port was too slow. Now it works properly.