ensure-json/dist/cli.js

A <3kB, dependency-free helper that repairs 'almost-JSON' text from LLMs and returns a valid JavaScript object—or throws JsonFixError.

#!/usr/bin/env node

// src/ensureJson.ts
var JsonFixError = class extends Error {
  constructor(msg, raw) {
    super(msg);
    this.name = "JsonFixError";
    this.raw = raw;
  }
};
function ensureJson(raw, schema) {
  let parsed;
  try {
    parsed = JSON.parse(raw);
  } catch {
    parsed = tryRepair(raw);
  }
  if (schema) {
    const result = schema.safeParse(parsed);
    if (!result.success) {
      throw new JsonFixError("Schema validation failed", raw);
    }
    return result.data;
  }
  return parsed;
}
function tryRepair(raw) {
  let text = raw;
  text = text.replace(/^\s*```(?:json)?|```\s*$/gim, "");
  const firstBrace = Math.min(
    ...["{", "["].map((c) => {
      const i = text.indexOf(c);
      return i === -1 ? Infinity : i;
    })
  );
  if (firstBrace !== Infinity) text = text.slice(firstBrace);
  text = text.replace(/,\s*([}\]])/g, "$1");
  text = text.replace(/'([^']+)':/g, (_, k) => `"${k}":`);
  text = text.replace(/([{,]\s*)([a-zA-Z0-9_]+)\s*:/g, '$1"$2":');
  const openBraces = (text.match(/{/g) || []).length;
  const closeBraces = (text.match(/}/g) || []).length;
  if (openBraces === closeBraces + 1) text += "}";
  const openBrackets = (text.match(/\[/g) || []).length;
  const closeBrackets = (text.match(/]/g) || []).length;
  if (openBrackets === closeBrackets + 1) text += "]";
  try {
    return JSON.parse(text);
  } catch (err) {
    throw new JsonFixError("Failed to repair and parse JSON", raw);
  }
}

// src/cli.ts
function readStdin() {
  return new Promise((resolve, reject) => {
    let data = "";
    process.stdin.setEncoding("utf8");
    process.stdin.on("data", (chunk) => data += chunk);
    process.stdin.on("end", () => resolve(data));
    process.stdin.on("error", reject);
  });
}
async function main() {
  if (process.argv.includes("--help")) {
    console.log(`Usage: json-fix [--help]
Reads JSON from stdin, repairs it, and writes valid JSON to stdout.
Exits 0 on success, 1 on failure.`);
    process.exit(0);
  }
  try {
    const input = await readStdin();
    const result = ensureJson(input);
    process.stdout.write(JSON.stringify(result, null, 2) + "\n");
    process.exit(0);
  } catch (err) {
    if (err instanceof JsonFixError) {
      process.stderr.write(`JsonFixError: ${err.message}
`);
    } else {
      process.stderr.write(`Error: ${String(err)}
`);
    }
    process.exit(1);
  }
}
main();