@jridgewell/trace-mapping 0.3.31: decodedMappings

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 @jridgewell/trace-mapping.decodedMappings in pkg:npm/%40jridgewell/trace-mapping@0.3.31
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/%40jridgewell/trace-mapping@0.3.31
Demonstrate these symbols/APIs:
  - @jridgewell/trace-mapping.decodedMappings
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:sha256:6666bafb3b3a0ae44070c09599de45d86fb958a09e7702fe4dca0254d5c2441c","constraints":{"executionContext":"node"},"contract":["decodedMappings returns the 2D array of decoded segments from a TraceMap initialized with encoded VLQ string","decodedMappings decodes 1-segment, 4-segment, and 5-segment mapping tokens into numeric tuples","decodedMappings produces an array entry for every generated line including lines without mappings","decodedMappings returns identical decoded mapping segments when initialized from decoded object or JSON string","decodedMappings decodes empty string mappings to a single line with empty segments and preserves empty array mappings","decodedMappings returns a consistent mapping structure across multiple calls on the same TraceMap instance"],"goal":"verify @jridgewell/trace-mapping.decodedMappings in pkg:npm/%40jridgewell/trace-mapping@0.3.31","kind":"HOW","packages":["pkg:npm/%40jridgewell/trace-mapping@0.3.31"],"schemaVersion":1,"symbols":["@jridgewell/trace-mapping.decodedMappings"]},"contractCommand":["node","test/contract.mjs"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"npm","executionContext":"node","language":"javascript","libc":"glibc","libcVersion":"2.39","moduleSystem":"esm","os":"linux","osVersionBucket":"24","packageManager":"npm","packageManagerVersion":"10.9.8","runtime":"node","runtimeVersion":"22.23.2","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/%40jridgewell/trace-mapping@0.3.31"],"schemaVersion":1,"subject":"pkg:npm/%40jridgewell/trace-mapping@0.3.31","symbols":["@jridgewell/trace-mapping.decodedMappings"],"verifierAdapter":"node-typescript@1"}

import { TraceMap, decodedMappings } from '@jridgewell/trace-mapping';

/**
 * Returns the decoded mappings array from a source map input or TraceMap instance.
 * @param {import('@jridgewell/trace-mapping').SourceMapInput | TraceMap} input
 * @returns {Readonly<import('@jridgewell/trace-mapping').DecodedSourceMap['mappings']>}
 */
export function getDecodedMappings(input) {
  const tracer = input instanceof TraceMap ? input : new TraceMap(input);
  return decodedMappings(tracer);
}

export { TraceMap, decodedMappings };
export default getDecodedMappings;

{
  "name": "sample-trace-mapping-decoded-mappings",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-trace-mapping-decoded-mappings",
      "version": "1.0.0",
      "license": "MIT-0",
      "dependencies": {
        "@jridgewell/trace-mapping": "0.3.31"
      }
    },
    "node_modules/@jridgewell/resolve-uri": {
      "version": "3.1.2",
      "resolved": "https://registry.npmjs.org/@jridgewell/resolve-uri/-/resolve-uri-3.1.2.tgz",
      "integrity": "sha512-bRISgCIjP20/tbWSPWMEi54QVPRZExkuD9lJL+UIxUKtwVJA8wW1Trb1jMs1RFXo1CBTNZ/5hpC9QvmKWdopKw==",
      "license": "MIT",
      "engines": {
        "node": ">=6.0.0"
      }
    },
    "node_modules/@jridgewell/sourcemap-codec": {
      "version": "1.5.5",
      "resolved": "https://registry.npmjs.org/@jridgewell/sourcemap-codec/-/sourcemap-codec-1.5.5.tgz",
      "integrity": "sha512-cYQ9310grqxueWbl+WuIUIaiUaDcj7WOq5fVhEljNVgRfOUhY9fy2zTvfoqWsnebh8Sl70VScFbICvJnLKB0Og==",
      "license": "MIT"
    },
    "node_modules/@jridgewell/trace-mapping": {
      "version": "0.3.31",
      "resolved": "https://registry.npmjs.org/@jridgewell/trace-mapping/-/trace-mapping-0.3.31.tgz",
      "integrity": "sha512-zzNR+SdQSDJzc8joaeP8QQoCQr8NuYx2dIIytl1QeBEZHJ9uW6hebsrYgbz8hJwUQao3TWCMtmfV8Nu1twOLAw==",
      "license": "MIT",
      "dependencies": {
        "@jridgewell/resolve-uri": "^3.1.0",
        "@jridgewell/sourcemap-codec": "^1.4.14"
      }
    }
  }
}

{
  "name": "sample-trace-mapping-decoded-mappings",
  "version": "1.0.0",
  "type": "module",
  "main": "index.js",
  "scripts": {
    "test": "node test/contract.mjs"
  },
  "dependencies": {
    "@jridgewell/trace-mapping": "0.3.31"
  },
  "license": "MIT-0"
}

{
  "schemaVersion": 1,
  "goal": "verify @jridgewell/trace-mapping.decodedMappings in pkg:npm/%40jridgewell/trace-mapping@0.3.31",
  "kind": "HOW",
  "packages": [
    "pkg:npm/%40jridgewell/trace-mapping@0.3.31"
  ],
  "symbols": [
    "@jridgewell/trace-mapping.decodedMappings"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

import assert from 'node:assert/strict';
import { TraceMap, decodedMappings, getDecodedMappings } from '../index.js';

// 1. decodedMappings returns the 2D array of decoded segments from a TraceMap initialized with encoded VLQ string
{
  const encodedMap = {
    version: 3,
    file: 'bundle.js',
    sources: ['src/app.js'],
    sourcesContent: ['console.log("hello");'],
    names: ['console', 'log'],
    mappings: 'AAAA,SAASA,GAAG',
    sourceRoot: 'http://example.com/'
  };

  const tracer = new TraceMap(encodedMap);
  const mappings = decodedMappings(tracer);

  assert.ok(Array.isArray(mappings));
  assert.equal(mappings.length, 1);
  assert.ok(Array.isArray(mappings[0]));
  assert.ok(mappings[0].length >= 2);
  assert.ok(Array.isArray(mappings[0][0]));
  assert.equal(typeof mappings[0][0][0], 'number');
}

// 2. decodedMappings decodes 1-segment, 4-segment, and 5-segment mapping tokens into numeric tuples
{
  const mapData = {
    version: 3,
    sources: ['orig.js'],
    names: ['myVar'],
    mappings: 'A;AAAA;AAAAA'
  };

  const tracer = new TraceMap(mapData);
  const mappings = decodedMappings(tracer);

  assert.equal(mappings.length, 3);
  assert.deepEqual(mappings[0][0], [0]);
  assert.deepEqual(mappings[1][0], [0, 0, 0, 0]);
  assert.deepEqual(mappings[2][0], [0, 0, 0, 0, 0]);
}

// 3. decodedMappings produces an array entry for every generated line including lines without mappings
{
  const mapData = {
    version: 3,
    sources: ['source.js'],
    names: [],
    mappings: 'AAAA;;AAAA'
  };

  const tracer = new TraceMap(mapData);
  const mappings = decodedMappings(tracer);

  assert.equal(mappings.length, 3);
  assert.equal(mappings[0].length, 1);
  assert.deepEqual(mappings[1], []);
  assert.equal(mappings[2].length, 1);
}

// 4. decodedMappings returns identical decoded mapping segments when initialized from decoded object or JSON string
{
  const rawDecoded = {
    version: 3,
    file: 'test.js',
    sources: ['test.ts'],
    names: ['alpha'],
    mappings: [
      [[0, 0, 0, 0]],
      [[4, 0, 1, 2, 0]]
    ]
  };

  const tracerFromDecoded = new TraceMap(rawDecoded);
  const mappings1 = decodedMappings(tracerFromDecoded);
  assert.deepEqual(mappings1, [
    [[0, 0, 0, 0]],
    [[4, 0, 1, 2, 0]]
  ]);

  const jsonStr = JSON.stringify(rawDecoded);
  const tracerFromJson = new TraceMap(jsonStr);
  const mappings2 = decodedMappings(tracerFromJson);
  assert.deepEqual(mappings2, [
    [[0, 0, 0, 0]],
    [[4, 0, 1, 2, 0]]
  ]);

  const helperMappings = getDecodedMappings(rawDecoded);
  assert.deepEqual(helperMappings, mappings1);
}

// 5. decodedMappings decodes empty string mappings to a single line with empty segments and preserves empty array mappings
{
  const emptyStringMap = {
    version: 3,
    sources: [],
    names: [],
    mappings: ''
  };
  const tracerEmptyStr = new TraceMap(emptyStringMap);
  const mappingsEmptyStr = decodedMappings(tracerEmptyStr);
  assert.equal(mappingsEmptyStr.length, 1);
  assert.deepEqual(mappingsEmptyStr[0], []);

  const emptyArrayMap = {
    version: 3,
    sources: [],
    names: [],
    mappings: []
  };
  const tracerEmptyArr = new TraceMap(emptyArrayMap);
  const mappingsEmptyArr = decodedMappings(tracerEmptyArr);
  assert.equal(mappingsEmptyArr.length, 0);
  assert.deepEqual(mappingsEmptyArr, []);
}

// 6. decodedMappings returns a consistent mapping structure across multiple calls on the same TraceMap instance
{
  const mapData = {
    version: 3,
    sources: ['a.js'],
    names: [],
    mappings: 'AAAA;ACAA'
  };

  const tracer = new TraceMap(mapData);
  const mappingsFirst = decodedMappings(tracer);
  const mappingsSecond = decodedMappings(tracer);

  assert.deepEqual(mappingsFirst, mappingsSecond);
  assert.equal(mappingsFirst.length, mappingsSecond.length);
  assert.deepEqual(mappingsFirst[0], mappingsSecond[0]);
  assert.deepEqual(mappingsFirst[1], mappingsSecond[1]);
}

console.log('Contract tests passed successfully.');