feat: ➕ add MarkWritable (#296)

* feat: ➕ add MarkWritable 🚀 * test: 🧪 MarkWritable * docs: ➕ add MarkWritable 📄 * docs: 📄 changeset * docs: 📄 fix typo in README * docs: 📄 update changeset
ts-essentials · Jan 31, 2022 · 6b27ee4 · 6b27ee4
1 parent fa03dda
commit 6b27ee4
Show file tree

Hide file tree

Showing 4 changed files with 67 additions and 0 deletions.
diff --git a/.changeset/pink-bats-invent.md b/.changeset/pink-bats-invent.md
@@ -0,0 +1,5 @@
+---
+"ts-essentials": minor
+---
+
+Add `MarkWritable` which unsets readonly for specified keys
diff --git a/README.md b/README.md
@@ -67,6 +67,7 @@ If you use any [functions](https://github.com/krzkaczor/ts-essentials/blob/maste
   - [MarkRequired](#MarkRequired)
   - [MarkOptional](#MarkOptional)
   - [MarkReadonly](#MarkReadonly)
+  - [MarkWritable](#MarkWritable)
   - [ReadonlyKeys](#ReadonlyKeys)
   - [WritableKeys](#WritableKeys)
   - [OptionalKeys](#OptionalKeys)
@@ -773,6 +774,30 @@ type UserThatCannotChangeName = MarkReadonly<User, "name">;
 // }
 ```
 
+### MarkWritable
+
+Useful when you want to make some properties writable (or unset `readonly`) without creating a separate type.
+
+```typescript
+interface User {
+  readonly id: number;
+  readonly name: string;
+  readonly email: string;
+  readonly password: string;
+}
+
+type UserThatCanChangeName = MarkWritable<User, "name">;
+
+// Result:
+
+// {
+//   readonly id: number;
+//   name: string;
+//   readonly email: string;
+//   readonly password: string;
+// }
+```
+
 ### ReadonlyKeys
 
 Gets keys of an object which are readonly.

diff --git a/lib/types.ts b/lib/types.ts
@@ -400,6 +400,9 @@ export type MarkOptional<T, K extends keyof T> = Omit<T, K> & Partial<Pick<T, K>
 /** Mark some properties as readonly, leaving others unchanged */
 export type MarkReadonly<T, K extends keyof T> = Omit<T, K> & Readonly<Pick<T, K>>;
 
+/** Mark some properties as writable, leaving others unchanged */
+export type MarkWritable<T, K extends keyof T> = Omit<T, K> & Writable<Pick<T, K>>;
+
 /** Convert union type to intersection #darkmagic */
 export type UnionToIntersection<U> = (U extends any ? (k: U) => void : never) extends (k: infer I) => void ? I : never;
 

diff --git a/test/mark-writable.ts b/test/mark-writable.ts
@@ -0,0 +1,34 @@
+import { AssertTrue as Assert, IsExact } from "conditional-type-checks";
+import { MarkWritable, Writable, ReadonlyKeys, WritableKeys } from "../lib/types";
+
+function testMarkWritable() {
+  type Example = {
+    readonly readonly1: Date;
+    readonly readonly2: RegExp;
+    required1: number;
+    required2: string;
+    optional1?: null;
+    optional2?: boolean;
+  };
+
+  type cases = [
+    Assert<IsExact<MarkWritable<Example, never>, Example>>,
+    Assert<IsExact<MarkWritable<Example, WritableKeys<Example>>, Example>>,
+    Assert<IsExact<MarkWritable<Example, ReadonlyKeys<Example>>, Writable<Example>>>,
+    Assert<
+      IsExact<
+        MarkWritable<Example, "readonly1">,
+        {
+          readonly1: Date;
+          readonly readonly2: RegExp;
+          required1: number;
+          required2: string;
+          optional1?: null;
+          optional2?: boolean;
+        }
+      >
+    >,
+    // @ts-expect-error do NOT support union types
+    MarkWritable<Example | { a: 1 }, "readonly1">,
+  ];
+}