CodeSampleX

Sample

typescript 7.0.2: Compute source code line starts and map text positions using computeLineStarts

Verified sample for npm typescript 7.0.2: Compute source code line starts and map text positions using computeLineStarts. The contract ran on node 22 · linux…

sha256:b31babca09bf9de0584f7f4edc5d7af3db347bfc2d06e19b56359d1290467626

This network offers one thing: a sample that builds. It ran the sample in a sandbox and kept the signed receipt. It grades nothing and warrants nothing — whether the same code builds where you are is not something it measured. How many distinct signing keys filed a passing contract receipt. One is the author alone; more than one means somebody else built it too. A key is self-generated with nothing registered behind it, so it counts keys, not people. MIT-0

Execution evidence

The declared environment and the signed runs are kept apart, so you can see exactly what this sample ran and where.

Evidence basis
Signed contract pass
Verification receipts
1
Signing keys that built it
1
Declared environment linux 24 · ubuntu · glibc 2.39 x64 npm

Verification-run environments

Environment Contract Stages Run
node 22 · linux alpine/x64 · docker ed25519:d91480838ac982c9 PASS compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS
CONTAINER_RUN · node-typescript@1		 2026-08-20

Case

HOW
Goal
Compute source code line starts and map text positions using computeLineStarts
Packages
Symbols
  • computeLineStarts
Created
2026-08-20T04:33:57Z

Contract

  1. computeLineStarts calculates 0-indexed line start offsets for multiline source code
  2. computeLineStarts handles various newline delimiters including CRLF and LF
  3. getPositionLineAndCharacter maps character offsets to line and character positions
  4. extractLineText retrieves the exact line content for a given line index

Files

  • PROMPT.md
  • csx.json
  • package-lock.json
  • package.json
  • spec.json
  • src/index.mjs
  • test/contract.mjs

Download the source artifact (tar.gz)

Source

PROMPT.md
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: Compute source code line starts and map text positions using computeLineStarts
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/typescript@7.0.2
Demonstrate these symbols/APIs:
  - computeLineStarts

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.
csx.json
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package-lock.json
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package.json
{
  "name": "typescript-computelinestarts-sample",
  "version": "1.0.0",
  "description": "Compute source code line starts and map text positions using computeLineStarts",
  "type": "module",
  "main": "src/index.mjs",
  "scripts": {
    "test": "node test/contract.mjs"
  },
  "dependencies": {
    "typescript": "7.0.2"
  },
  "license": "MIT-0"
}
spec.json
{
  "schemaVersion": 1,
  "goal": "Compute source code line starts and map text positions using computeLineStarts",
  "kind": "HOW",
  "packages": [
    "pkg:npm/typescript@7.0.2"
  ],
  "symbols": [
    "computeLineStarts"
  ]
}
src/index.mjs
import { computeLineStarts } from 'typescript/unstable/ast';

/**
 * Computes the 0-indexed line start offsets for a given source code string.
 *
 * @param {string} text - Source code text.
 * @returns {number[]} Array of 0-indexed character offsets where each line begins.
 */
export function getLineStarts(text) {
  if (typeof text !== 'string') {
    throw new TypeError('Expected text to be a string');
  }
  return computeLineStarts(text);
}

/**
 * Maps a 0-indexed character position to a 0-indexed line and character (column) position.
 *
 * @param {readonly number[]} lineStarts - Line start offsets computed by computeLineStarts.
 * @param {number} position - 0-indexed character offset in the source text.
 * @returns {{ line: number, character: number }}
 */
export function getPositionLineAndCharacter(lineStarts, position) {
  if (!Array.isArray(lineStarts) || lineStarts.length === 0) {
    throw new Error('Invalid lineStarts array');
  }
  if (typeof position !== 'number' || position < 0) {
    throw new Error('Position must be a non-negative number');
  }

  let low = 0;
  let high = lineStarts.length - 1;

  while (low <= high) {
    const mid = Math.floor((low + high) / 2);
    const start = lineStarts[mid];

    if (start === position) {
      return { line: mid, character: 0 };
    } else if (start < position) {
      low = mid + 1;
    } else {
      high = mid - 1;
    }
  }

  const line = high >= 0 ? high : 0;
  const character = position - lineStarts[line];
  return { line, character };
}

/**
 * Extracts the exact line content for a given 0-indexed line number.
 *
 * @param {string} sourceText - Full source text.
 * @param {readonly number[]} lineStarts - Line start offsets.
 * @param {number} lineIndex - 0-indexed line index.
 * @returns {string} Text of the requested line.
 */
export function extractLineText(sourceText, lineStarts, lineIndex) {
  if (lineIndex < 0 || lineIndex >= lineStarts.length) {
    throw new RangeError(`Line index ${lineIndex} out of bounds`);
  }
  const start = lineStarts[lineIndex];
  const end = lineIndex + 1 < lineStarts.length ? lineStarts[lineIndex + 1] : sourceText.length;
  return sourceText.slice(start, end);
}

/**
 * Returns the total line count for the source text.
 *
 * @param {readonly number[]} lineStarts - Line start offsets.
 * @returns {number} Number of lines.
 */
export function getLineCount(lineStarts) {
  return lineStarts.length;
}

export { computeLineStarts };
test/contract.mjs
import assert from 'node:assert/strict';
import {
  computeLineStarts,
  getLineStarts,
  getPositionLineAndCharacter,
  extractLineText,
  getLineCount,
} from '../src/index.mjs';

// Contract 1: computeLineStarts calculates 0-indexed line start offsets for multiline source code
{
  const source = 'function greet(name: string): string {\n  return `Hello, ${name}!`;\n}\n';
  const lineStarts = computeLineStarts(source);
  assert.ok(Array.isArray(lineStarts), 'Line starts must be an array');
  assert.strictEqual(lineStarts[0], 0, 'First line starts at offset 0');
  assert.strictEqual(lineStarts[1], 39, 'Second line starts after first newline');
  assert.strictEqual(lineStarts[2], 67, 'Third line starts after second newline');
  assert.strictEqual(lineStarts[3], 69, 'Fourth line starts after third newline');
  assert.strictEqual(getLineCount(lineStarts), 4, 'Total line count should match array length');
}

// Contract 2: computeLineStarts handles various newline delimiters including CRLF and LF
{
  const unixText = 'first\nsecond\nthird';
  const unixStarts = computeLineStarts(unixText);
  assert.deepStrictEqual(unixStarts, [0, 6, 13], 'Unix LF line starts match');

  const winText = 'first\r\nsecond\r\nthird';
  const winStarts = computeLineStarts(winText);
  assert.deepStrictEqual(winStarts, [0, 7, 15], 'Windows CRLF line starts match');

  const singleLine = 'hello world';
  const singleStarts = computeLineStarts(singleLine);
  assert.deepStrictEqual(singleStarts, [0], 'Single line without newline has start at 0');

  const emptyText = '';
  const emptyStarts = computeLineStarts(emptyText);
  assert.deepStrictEqual(emptyStarts, [0], 'Empty text has one line start at 0');
}

// Contract 3: getPositionLineAndCharacter maps character offsets to line and character positions
{
  const source = 'line zero\nline one\nline two';
  const lineStarts = getLineStarts(source);

  const pos0 = getPositionLineAndCharacter(lineStarts, 0);
  assert.strictEqual(pos0.line, 0);
  assert.strictEqual(pos0.character, 0);

  const pos5 = getPositionLineAndCharacter(lineStarts, 5);
  assert.strictEqual(pos5.line, 0);
  assert.strictEqual(pos5.character, 5);

  const pos10 = getPositionLineAndCharacter(lineStarts, 10);
  assert.strictEqual(pos10.line, 1);
  assert.strictEqual(pos10.character, 0);

  const pos15 = getPositionLineAndCharacter(lineStarts, 15);
  assert.strictEqual(pos15.line, 1);
  assert.strictEqual(pos15.character, 5);

  const pos19 = getPositionLineAndCharacter(lineStarts, 19);
  assert.strictEqual(pos19.line, 2);
  assert.strictEqual(pos19.character, 0);
}

// Contract 4: extractLineText retrieves the exact line content for a given line index
{
  const source = 'const x: number = 42;\nconst y: string = "test";\nconsole.log(x, y);\n';
  const lineStarts = getLineStarts(source);

  const line0 = extractLineText(source, lineStarts, 0);
  assert.strictEqual(line0, 'const x: number = 42;\n');

  const line1 = extractLineText(source, lineStarts, 1);
  assert.strictEqual(line1, 'const y: string = "test";\n');

  const line2 = extractLineText(source, lineStarts, 2);
  assert.strictEqual(line2, 'console.log(x, y);\n');

  const line3 = extractLineText(source, lineStarts, 3);
  assert.strictEqual(line3, '');

  assert.throws(() => {
    extractLineText(source, lineStarts, -1);
  }, RangeError);

  assert.throws(() => {
    extractLineText(source, lineStarts, 99);
  }, RangeError);
}

console.log('All pkg:npm/typescript@7.0.2 computeLineStarts contracts passed.');

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