docs(partition): add an overload for better typing (#5756)

* docs(partition): add an overload for better typing * refactor: add thisArg support * test: add dtslint tests * chore: update api_guardian Co-authored-by: Nicholas Jamieson <[email protected]>
ReactiveX · Mar 18, 2021 · acdab5c · acdab5c
1 parent dd307ce
commit acdab5c
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Showing 3 changed files with 24 additions and 4 deletions.
diff --git a/api_guard/dist/types/index.d.ts b/api_guard/dist/types/index.d.ts
@@ -321,6 +321,8 @@ export declare function pairs(n: number | bigint | boolean | ((...args: any[]) =
 
 export declare type PartialObserver<T> = NextObserver<T> | ErrorObserver<T> | CompletionObserver<T>;
 
+export declare function partition<T, U extends T, A>(source: ObservableInput<T>, predicate: (this: A, value: T, index: number) => value is U, thisArg: A): [Observable<U>, Observable<T>];
+export declare function partition<T, U extends T>(source: ObservableInput<T>, predicate: (value: T, index: number) => value is U): [Observable<U>, Observable<T>];
 export declare function partition<T, A>(source: ObservableInput<T>, predicate: (this: A, value: T, index: number) => boolean, thisArg: A): [Observable<T>, Observable<T>];
 export declare function partition<T>(source: ObservableInput<T>, predicate: (value: T, index: number) => boolean): [Observable<T>, Observable<T>];
 

diff --git a/spec-dtslint/observables/partition-spec.ts b/spec-dtslint/observables/partition-spec.ts
@@ -5,8 +5,8 @@ it('should infer correctly', () => {
   const p = partition(of('a', 'b', 'c'), () => true); // $ExpectType [Observable<string>, Observable<string>]
 });
 
-it('should accept a thisArg parameter', () => {
-  const o = partition(of('a', 'b', 'c'), () => true, 5); // $ExpectType [Observable<string>, Observable<string>]
+it('should support a user-defined type guard', () => {
+  const o = partition(of(1, 2, 3), (value: number): value is 1 => value === 1); // $ExpectType [Observable<1>, Observable<number>]
 });
 
 it('should enforce predicate', () => {
@@ -19,9 +19,17 @@ it('should enforce predicate types', () => {
   const q = partition(of('a', 'b', 'c'), (value, index: string) => true); // $ExpectError
 });
 
-it('should support this', () => {
+it('should support this with type guard', () => {
   const thisArg = { limit: 2 };
-  const a = partition(of(1, 2, 3), function (val) {
+  const a = partition(of(1, 2, 3), function (val): val is 1 { // $ExpectType [Observable<1>, Observable<number>]
+    const limit = this.limit; // $ExpectType number
+    return val < limit;
+  }, thisArg);
+});
+
+it('should support this with predicate', () => {
+  const thisArg = { limit: 2 };
+  const a = partition(of(1, 2, 3), function (val) { // $ExpectType [Observable<number>, Observable<number>]
     const limit = this.limit; // $ExpectType number
     return val < limit;
   }, thisArg);

diff --git a/src/internal/observable/partition.ts b/src/internal/observable/partition.ts
@@ -4,6 +4,16 @@ import { ObservableInput } from '../types';
 import { Observable } from '../Observable';
 import { innerFrom } from './from';
 
+export function partition<T, U extends T, A>(
+  source: ObservableInput<T>,
+  predicate: (this: A, value: T, index: number) => value is U,
+  thisArg: A
+): [Observable<U>, Observable<T>];
+export function partition<T, U extends T>(
+  source: ObservableInput<T>,
+  predicate: (value: T, index: number) => value is U
+): [Observable<U>, Observable<T>];
+
 export function partition<T, A>(
   source: ObservableInput<T>,
   predicate: (this: A, value: T, index: number) => boolean,