1️⃣
✅ string + string | number => string
❌ number + string | number => error 2365

▶️ Playground

2️⃣
❌ No error firing on generic wrong return type.

▶️ Playground

3️⃣
❌ Type guard wrong types intersection via casting to unknown.

▶️ Playground

4️⃣
🤔 Guarded type narrowing.

▶️ Playground

5️⃣
🧐 A bit more complex guarded type.

▶️ Playground

6️⃣
❌ Inaccurate "1/1" | "2/2" type inference.

▶️ Playground

7️⃣
❌ No errors when mutating tuples by number index.

▶️ Playground

8️⃣
❌ Interface doesn't fit Record<string, unknown>.

▶️ Playground

9️⃣
🤯 Type any passes extends operator along both branches.

▶️ Playground

🔟
❌ Brand as key of Record might be type unsafe.
▶️ Playground

🤨 But Flavour as key of Record is just OK.
▶️ Playground