Before You File a Bug Report Please Confirm You Have Done The Following...

• I have tried restarting my IDE and the issue persists.
• I have updated to the latest version of the packages.
• I have searched for related issues and found none that matched my issue.
• I have read the FAQ and my problem is not listed.

Playground Link

https://typescript-eslint.io/play/#ts=5.6.3&fileType=.tsx&code=CYUwxgNghgTiAEYD2A7AzgF3gMyhNIAngEICWA5gJIoYBc8ADCgNwBQp28AFLvkWVRoBKeAG9WAXyA&eslintrc=N4KABGBEBOCuA2BTAzpAXGUEKQAIBcBPABxQGNoBLY-AWhXkoDt8B6Jge1tiacTJTIAhtEK0yHJgBNK%2BSpPRQA7iKaRwYAL4hNQA&tsconfig=N4KABGBEDGD2C2AHAlgGwKYCcDyiAuysAdgM6QBcYoEEkJemy0eAcgK6qoDCAFutAGsylBm3TgwAXxCSgA&tokens=false

Repro Code

declare const falseyBigInt: 0n;
if (falseyBigInt) {
}

ESLint Config

module.exports = {
  "rules": {
    "@typescript-eslint/no-unnecessary-condition": "warn"
  }
}

tsconfig

{
  "compilerOptions": {
    "strictNullChecks": true
  }
}

Expected Result

Unnecessary conditional, value is always falsy.

Actual Result

Unnecessary conditional, value is always truthy.

Additional Info

This is a bug with this line.

The .value field returns a PseudoBigInt object that looks like { negative?: boolean, base10Value: string }, rather than a bigint itself (for legacy TS support reasons). So checking for truthiness is incorrect; we need to convert to a real bigint.