Fix: JSON Number Precision

The Precision Loss in Action

// Twitter-style ID — 19 digits, exceeds MAX_SAFE_INTEGER
const json = '{"id": 1234567890123456789}';

const parsed = JSON.parse(json);
console.log(parsed.id);
// => 1234567890123456800   ← WRONG — last digits changed!

// Verify the problem
console.log(Number.MAX_SAFE_INTEGER);
// => 9007199254740991

console.log(1234567890123456789 > Number.MAX_SAFE_INTEGER);
// => true  → precision loss is guaranteed

Float64 Number Range Reference

Solutions

Solution 1 — Use Strings for Large IDs (Recommended)

The simplest and most portable fix: serialize large integers as JSON strings. All clients receive the exact digits regardless of their number type.

{"id": 1234567890123456789}

{"id": "1234567890123456789"}

Solution 2 — BigInt Reviver

If you receive JSON you cannot change, parse numbers as strings first then convert to BigInt:

// Replace large integers with quoted strings before parsing
function parseWithBigInt(jsonString: string) {
  // Match integers with more than 15 digits (safely over MAX_SAFE_INTEGER)
  const safe = jsonString.replace(
    /:\s*(-?\d{16,})/g,
    ': "$1"'
  );
  return JSON.parse(safe, (key, val) => {
    if (typeof val === "string" && /^-?\d{16,}$/.test(val)) {
      return BigInt(val);
    }
    return val;
  });
}

const result = parseWithBigInt('{"id": 1234567890123456789}');
console.log(result.id);         // 1234567890123456789n (BigInt, exact)
console.log(typeof result.id);  // "bigint"

Solution 3 — json-bigint Library

The json-bigint npm package is a drop-in replacement that handles large integers automatically:

import JSONbig from "json-bigint";

const parsed = JSONbig.parse('{"id": 1234567890123456789}');
console.log(parsed.id.toString());
// => "1234567890123456789"  — exact

Inspect Your JSON Below

Paste JSON containing large numbers to see how JavaScript parses them.