Object is possibly 'null' when using type guard for for loops

[fzn0x]

🔍 Search Terms

if ((uploaded || []).length !== 0) {
  for (let data of uploaded) { // -> this line throws let uploaded: unknown[] | null 'uploaded' is possibly 'null'.ts(18047)
  }
}

✅ Viability Checklist

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)
• This isn't a request to add a new utility type: https://github.com/microsoft/TypeScript/wiki/No-New-Utility-Types
• This feature would agree with the rest of our Design Goals: https://github.com/Microsoft/TypeScript/wiki/TypeScript-Design-Goals

⭐ Suggestion

Should not throw

📃 Motivating Example

💻 Use Cases

[fatcerberus]

This is kind of an odd construction. At any rate TS can't tell that [].length is always 0 (it's just checking the .length of something with an array type, which in general could be anything) so as far as the compiler is concerned uploaded could still be nullish after this check

[fzn0x]

Thanks for tracking this as "Design Limitation". 👍