What this snippet does
If no members of the union match, Extract results in the 'never' type, making variables unassignable.
Expected output
Compile Error: Type 'any' is not assignable to type 'never'.
Why practise typing this
Typing utility types code builds muscle memory for the symbols and indentation TypeScript uses most, which prose-based typing tests never cover. DevType measures your words per minute and accuracy on this snippet and tracks the individual characters you mistype, so later lessons can target them.
More TypeScript practice
- Making all properties optional with PartialUtility Types · intermediate
- Updating user profiles with patch payloadsUtility Types · intermediate
- Assuming Required unmakes optional properties during runtimeUtility Types · intermediate
- Making all properties readonlyUtility Types · intermediate
- Creating an immutable configuration objectUtility Types · intermediate
- Mutating a Readonly type via aliasingUtility Types · intermediate