In future (at least after seeing how it goes after the origin trial on Chrome), it might be a good idea to introduce an option like useExperimentalJSStringBuiltins, and if this option is turned ON, generate a WebAssembly module that implements JavaScript string operations using the js-string-builtins proposals.

What is the js-string-builtins proposal

The js-string-builtin proposal aims to improve the efficiency of string operations by allowing us to directly use a subset of the JS String API through built-in WebAssembly functions. These builtin functions can be efficiently called from within WebAssembly modules without the need for JS glue code, the implementations are provided by the Wasm runtime. (This import mechanism is said to be more efficient than regular imports)

We can use these builtin functions by giving a WebAssemblyCompileOptions like this:

WebAssembly.compile(bytes, { builtins: ['js-string'] });

The builtin functions include (from|into)CharCodeArray to convert i16array <=> externref (js string), cast, test, and so on

(This proposal also provides a way to encode/decode UTF-8 strings through wasm:text-encoder and wasm:text-decoder)

Why

For example, instead of converting individual character codes using String.fromCharCode and concatenating them in genCreateStringFromData

the "wasm:js-string" "fromCharCodeArray" builtin function can be used to convert an i16array directly to a JavaScript string more efficiently.

/// Convert the specified range of a mutable i16 array into a String,
/// treating each i16 as an unsigned 16-bit char code.
///
/// The range is given by [start, end). This function traps if the range is
/// outside the bounds of the array.
///
/// NOTE: This function only takes a mutable i16 array defined in its own
/// recursion group.
///
/// If this is an issue for toolchains, we can look into how to relax the
/// function type while still maintaining good performance.
func fromCharCodeArray(
  array: (ref null (array (mut i16))),
  start: i32,
  end: i32
) -> (ref extern)

https://github.com/WebAssembly/js-string-builtins/blob/main/proposals/js-string-builtins/Overview.md#wasmjs-string-fromcharcodearray

Also, the builtin functions should be called more efficiently than imported functions, and we can expect some more efficient string operations.

When to work on it

Not now, we should see how it goes after the Origin trial

• At 2024-06-03, the proposal is still on origin trial in Chrome (119 to 127)
  • WebAssembly JS String Builtins - Chrome Platform Status
  • Intent to Experiment: WebAssembly JS String Builtins it seems like it's being tested on J2Wasm for Google Sheets.
• Available on V8
  • wasm-imported-strings Support compile-time imports · v8/v8@fb9a925 with --experimental-wasm-imported-strings?
  • from 12.2.279 (node.js v22 already on that version)
• spidermonkey 1863794 - Implement js-string-builtins proposal already supported?
• webkit: not yet.