How do you implement DeepPartial ? type DeepPartial = T extends object ? { [K in keyof T]?: DeepPartial } : T;

With a recursive mapped type that adds ? at every level

With the built-in utility Partial from lib.d.ts

You can't: recursive type aliases are forbidden in TypeScript

TypeScript · Senior · Question 6 of 75

How do you implement `DeepPartial<T>`?

type DeepPartial<T> = T extends object
  ? { [K in keyof T]?: DeepPartial<T[K]> }
  : T;

✓Correct answer: With a recursive mapped type that adds ? at every level
2With the built-in utility Partial<T, 'deep'> from lib.d.ts
3You can't: recursive type aliases are forbidden in TypeScript

Explanation

Type aliases can reference themselves. A real implementation should handle arrays, functions and Date separately so they aren't "broken down" into properties. Deep recursion has an instantiation limit, so huge types slow down the compiler.

How do you implement `DeepPartial<T>`?

Explanation

Further reading

Problem with a question

Test yourself

How do you implement DeepPartial<T>?

Explanation

Further reading

Test yourself

How do you implement `DeepPartial<T>`?