demo · v130

String Ops Bench

Chrome 130 ships WebAssembly JS String Builtins — Wasm functions that directly call JavaScript's built-in string methods without importing them from JS. This benchmark runs common string operations (concat, slice, search, compare, charCode) using the native JS path, simulates what the Wasm built-in version replaces, and shows relative throughput.

Checking WebAssembly JS String Builtins support…
100K
50 chars
Click Run benchmark to start.

Wasm string access methods compared

MethodNo builtins (pre-130)JS String Builtins (130)Speedup source
String.concat / + Import JS glue function Direct Wasm builtin Eliminates JS↔Wasm boundary crossing
String.length Import or extern ref Inline length check No function call overhead
charCodeAt / codePointAt JS import + coercion Direct memory read Avoids string boxing/unboxing
substring / slice JS import required Built-in call Avoids extern ref indirection
Comparison (===) JS import Builtin eq check Fast interned string comparison
Type (stringref) externref only WasmGC stringref type No GC pressure from extern wrapping 
// WebAssembly JS String Builtins (Chrome 130)
// WAT — access JS String methods directly

(module
  (import "wasm:js-string" "concat"      (func $concat      (param stringref stringref) (result stringref)))
  (import "wasm:js-string" "charCodeAt"  (func $charCodeAt  (param stringref i32) (result i32)))
  (import "wasm:js-string" "substring"   (func $substring   (param stringref i32 i32) (result stringref)))
  (import "wasm:js-string" "equals"      (func $equals      (param stringref stringref) (result i32)))
  (import "wasm:js-string" "length"      (func $length      (param stringref) (result i32)))

  ;; Equivalent JavaScript (pre-130 Wasm approach via import object)
  ;; { "js": { "concat": (a, b) => a + b, ... } }
  ;; Chrome 130: "wasm:js-string" namespace maps to engine-native builtins
  ;; No JS import object needed at instantiation time
)

// Instantiate with builtins enabled
const { instance } = await WebAssembly.instantiateStreaming(
  fetch('module.wasm'),
  {}, // No JS glue imports needed for wasm:js-string
  { builtins: ['js-string'] }   // Chrome 130
);

see also