Implement a generic `DeepReadonly<T>` which makes every parameter of an object - and its sub-objects recursively - readonly. Learn readonly modifiers in this medium-level challenge on TypeScriptPro.
In this medium-level challenge, you'll implement a generic DeepReadonly<T>, which makes every parameter of an object - and its sub-objects recursively - readonly.
Implement a generic DeepReadonly<T> which make every parameter of an object - and its sub-objects recursively - readonly.
You can assume that we are only dealing with Objects in this challenge. Arrays, Functions, Classes and so on do not need to be taken into consideration. However, you can still challenge yourself by covering as many different cases as possible.
For example:
type X = {
x: {
a: 1
b: 'hi'
}
y: 'hey'
}
type Expected = {
readonly x: {
readonly a: 1
readonly b: 'hi'
}
readonly y: 'hey'
}
type Todo = DeepReadonly<X> // should be same as `Expected`Change the following code to make the test cases pass (no type check errors).
To make an object deeply readonly, we need recursion:
type DeepReadonly<T> = T extends Function
? T
: {
readonly [K in keyof T]: DeepReadonly<T[K]>
}How it works:
Function, leave it as isT and applies the readonly modifier to themDeepReadonly type is applied recursively to the values of the type TThis challenge helps you understand readonly modifiers and how to apply this concept in real-world scenarios.
This challenge is originally from here.