@webassemblyjs/utf8 1.13.2: decode, encode

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify pkg:npm/%40webassemblyjs/utf8@1.13.2
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/%40webassemblyjs/utf8@1.13.2
Constraints:
  - executionContext: node
Required runtime conditions:
  - ecosystem: npm
  - language: javascript
  - moduleSystem: cjs
  - packageManager: npm@10.9.8
  - runtime: node@22.23.2

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

{"case":{"caseId":"case:sha256:f56e2b5d1996ea6b0e81dad7ce5f315ba9a08a7fa4ea29f98473bdb406c05dee","constraints":{"executionContext":"node"},"contract":["encode converts an ASCII string to an array of UTF-8 byte numbers and decode restores the original ASCII string","encode converts multi-byte Unicode characters into valid 2-byte and 3-byte UTF-8 sequences and decode reconstructs them","encode converts an empty string to an empty byte array and decode converts an empty byte array to an empty string","decode throws an error matching 'invalid UTF-8 encoding' when encountering invalid UTF-8 byte sequences or incomplete multi-byte sequences"],"goal":"verify pkg:npm/%40webassemblyjs/utf8@1.13.2","kind":"HOW","packages":["pkg:npm/%40webassemblyjs/utf8@1.13.2"],"schemaVersion":1,"symbols":["@webassemblyjs/utf8.decode","@webassemblyjs/utf8.encode"]},"contractCommand":["node","test/contract.cjs"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"npm","executionContext":"node","language":"javascript","libc":"glibc","libcVersion":"2.39","moduleSystem":"cjs","os":"linux","osVersionBucket":"24","packageManager":"npm","packageManagerVersion":"10.9.8","runtime":"node","runtimeVersion":"22.23.2","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/%40webassemblyjs/utf8@1.13.2"],"schemaVersion":1,"subject":"pkg:npm/%40webassemblyjs/utf8@1.13.2","symbols":["@webassemblyjs/utf8.decode","@webassemblyjs/utf8.encode"],"verifierAdapter":"node-typescript@1"}

{
  "name": "sample-webassemblyjs-utf8",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-webassemblyjs-utf8",
      "version": "1.0.0",
      "dependencies": {
        "@webassemblyjs/utf8": "1.13.2"
      }
    },
    "node_modules/@webassemblyjs/utf8": {
      "version": "1.13.2",
      "resolved": "https://registry.npmjs.org/@webassemblyjs/utf8/-/utf8-1.13.2.tgz",
      "integrity": "sha512-3NQWGjKTASY1xV5m7Hr0iPeXD9+RDobLll3T9d2AO+g3my8xy5peVyjSag4I50mR1bBSN/Ct12lo+R9tJk0NZQ==",
      "license": "MIT"
    }
  }
}

{
  "name": "sample-webassemblyjs-utf8",
  "version": "1.0.0",
  "private": true,
  "description": "Clean-room verification of @webassemblyjs/utf8",
  "dependencies": {
    "@webassemblyjs/utf8": "1.13.2"
  }
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:npm/%40webassemblyjs/utf8@1.13.2",
  "kind": "HOW",
  "packages": [
    "pkg:npm/%40webassemblyjs/utf8@1.13.2"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

'use strict';

const assert = require('node:assert/strict');
const { encode, decode } = require('@webassemblyjs/utf8');

// 1. encode converts an ASCII string to an array of UTF-8 byte numbers and decode restores the original ASCII string
const asciiStr = 'Hello, WebAssembly!';
const asciiBytes = encode(asciiStr);
assert.deepEqual(asciiBytes, [72, 101, 108, 108, 111, 44, 32, 87, 101, 98, 65, 115, 115, 101, 109, 98, 108, 121, 33]);
assert.equal(decode(asciiBytes), asciiStr);

// 2. encode converts multi-byte Unicode characters into valid 2-byte and 3-byte UTF-8 sequences and decode reconstructs them
const multiByteStr = '© €';
const multiByteBytes = encode(multiByteStr);
assert.deepEqual(multiByteBytes, [0xc2, 0xa9, 0x20, 0xe2, 0x82, 0xac]);
assert.equal(decode(multiByteBytes), multiByteStr);

// 3. encode converts an empty string to an empty byte array and decode converts an empty byte array to an empty string
assert.deepEqual(encode(''), []);
assert.equal(decode([]), '');

// 4. decode throws an error matching 'invalid UTF-8 encoding' when encountering invalid UTF-8 byte sequences or incomplete multi-byte sequences
assert.throws(() => decode([0x80]), /invalid UTF-8 encoding/);
assert.throws(() => decode([0xc2]), /invalid UTF-8 encoding/);
assert.throws(() => decode([0xe2, 0x82]), /invalid UTF-8 encoding/);

console.log('Contract test passed.');