Improved Optional type to better handle few edge cases

piotrwitek · May 7, 2019 · 8f1adf8 · 8f1adf8
1 parent 5125de8
commit 8f1adf8
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Showing 7 changed files with 112 additions and 60 deletions.
diff --git a/package-lock.json b/package-lock.json
diff --git a/package.json b/package.json
@@ -36,7 +36,7 @@
   "devDependencies": {
     "@types/jest": "21.1.10",
     "dts-jest": "22.0.4",
-    "husky": "1.3.1",
+    "husky": "2.2.0",
     "jest": "21.2.1",
     "prettier": "1.17.0",
     "ts-jest": "23.10.5",

diff --git a/src/__snapshots__/mapped-types.spec.ts.snap b/src/__snapshots__/mapped-types.spec.ts.snap
@@ -126,9 +126,13 @@ exports[`OmitByValueExact testType<OmitByValueExact<RequiredOptionalProps, undef
 
 exports[`OmitByValueExact testType<OmitByValueExact<T, number>>() 1`] = `"Pick<T, { [Key in keyof T]: [number] extends [T[Key]] ? [T[Key]] extends [T[Key] & number] ? never : Key : Key; }[keyof T]>"`;
 
-exports[`Optional testType<Optional<Props, 'age' | 'visible'>>() 1`] = `"(Pick<Props, \\"name\\" | \\"visible\\"> & { age?: number | undefined; }) | (Pick<Props, \\"name\\" | \\"age\\"> & { visible?: boolean | undefined; })"`;
+exports[`Optional testType<Optional<Props, 'age' | 'visible'>>({ name: 'Yolo' }) 1`] = `"Optional<Props, \\"age\\" | \\"visible\\">"`;
 
-exports[`Optional testType<Optional<Props>>() 1`] = `"Partial<Props>"`;
+exports[`Optional testType<Optional<Props, 'age' | 'visible'>>({ name: 'Yolo', age: 99 }) 1`] = `"Optional<Props, \\"age\\" | \\"visible\\">"`;
+
+exports[`Optional testType<Optional<Props>>({ age: 99 }) 1`] = `"Optional<Props, \\"name\\" | \\"age\\" | \\"visible\\">"`;
+
+exports[`Optional testType<Optional<Props>>({}) 1`] = `"Optional<Props, \\"name\\" | \\"age\\" | \\"visible\\">"`;
 
 exports[`OptionalKeys testType<OptionalKeys<RequiredOptionalProps>>() 1`] = `"\\"opt\\" | \\"optUndef\\""`;
 

diff --git a/src/mapped-types.spec.snap.ts b/src/mapped-types.spec.snap.ts
@@ -486,9 +486,13 @@ type RequiredOptionalProps = {
 
 // @dts-jest:group Optional
 {
-  // @dts-jest:pass:snap -> Partial<Props>
-  testType<Optional<Props>>();
-
-  // @dts-jest:pass:snap -> (Pick<Props, "name" | "visible"> & { age?: number | undefined; }) | (Pick<Props, "name" | "age"> & { visible?: boolean | undefined; })
-  testType<Optional<Props, 'age' | 'visible'>>();
+  // @dts-jest:pass:snap -> Optional<Props, "name" | "age" | "visible">
+  testType<Optional<Props>>({});
+  // @dts-jest:pass:snap -> Optional<Props, "name" | "age" | "visible">
+  testType<Optional<Props>>({ age: 99 });
+
+  // @dts-jest:pass:snap -> Optional<Props, "age" | "visible">
+  testType<Optional<Props, 'age' | 'visible'>>({ name: 'Yolo' });
+  // @dts-jest:pass:snap -> Optional<Props, "age" | "visible">
+  testType<Optional<Props, 'age' | 'visible'>>({ name: 'Yolo', age: 99 });
 }
diff --git a/src/mapped-types.spec.ts b/src/mapped-types.spec.ts
@@ -487,8 +487,12 @@ type RequiredOptionalProps = {
 // @dts-jest:group Optional
 {
   // @dts-jest:pass:snap
-  testType<Optional<Props>>();
+  testType<Optional<Props>>({});
+  // @dts-jest:pass:snap
+  testType<Optional<Props>>({ age: 99 });
 
   // @dts-jest:pass:snap
-  testType<Optional<Props, 'age' | 'visible'>>();
+  testType<Optional<Props, 'age' | 'visible'>>({ name: 'Yolo' });
+  // @dts-jest:pass:snap
+  testType<Optional<Props, 'age' | 'visible'>>({ name: 'Yolo', age: 99 });
 }
diff --git a/src/mapped-types.ts b/src/mapped-types.ts
@@ -150,6 +150,12 @@ export type ReadonlyKeys<T extends object> = {
   >
 }[keyof T];
 
+type IfEquals<X, Y, A = X, B = never> = (<T>() => T extends X
+  ? 1
+  : 2) extends (<T>() => T extends Y ? 1 : 2)
+  ? A
+  : B;
+
 /**
  * RequiredKeys
  * @desc get union type of keys that are required in object type `T`
@@ -527,12 +533,6 @@ export interface _DeepPartialArray<T> extends Array<DeepPartial<T>> {}
 /** @private */
 export type _DeepPartialObject<T> = { [P in keyof T]?: DeepPartial<T[P]> };
 
-type IfEquals<X, Y, A = X, B = never> = (<T>() => T extends X
-  ? 1
-  : 2) extends (<T>() => T extends Y ? 1 : 2)
-  ? A
-  : B;
-
 /**
  * Brand
  * @desc Define nominal type of U based on type of T.
@@ -571,6 +571,8 @@ export type Brand<T, U> = T & { __brand: U };
  *    // Expect: { name: string; age?: number; visible?: boolean; }
  *    type Props = Optional<Props, 'age' | 'visible'>;
  */
-export type Optional<T extends object, K = keyof any> = K extends (keyof T)
-  ? (Omit<T, K> & { [key in K]?: T[key] })
-  : Partial<T>;
+export type Optional<T extends object, K extends keyof T = keyof T> = Omit<
+  T,
+  K
+> &
+  Partial<Pick<T, K>>;
diff --git a/utils/test-utils.ts b/utils/test-utils.ts
@@ -1,5 +1,5 @@
 /** @internal */
-export function testType<T>(): T {
+export function testType<T>(a?: T): T {
   return undefined as any;
 }