New Feature: make Record.hasOwnProperty a type guard

gcanti · Jan 7, 2020 · 38d78c4 · 38d78c4
1 parent add2ffa
commit 38d78c4
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Showing 3 changed files with 25 additions and 4 deletions.
diff --git a/docs/modules/Record.ts.md b/docs/modules/Record.ts.md
@@ -353,14 +353,14 @@ Added in v2.0.0
 **Signature**
 
 ```ts
-export function hasOwnProperty<K extends string>(k: K, r: Record<K, unknown>): boolean { ... }
+export function hasOwnProperty<K extends string>(k: string, r: Record<K, unknown>): k is K { ... }
 ```
 
 Added in v2.0.0
 
 # insertAt (function)
 
-Insert or replace a key/value pair in a map
+Insert or replace a key/value pair in a record
 
 **Signature**
 

diff --git a/dtslint/ts3.5/Record.ts b/dtslint/ts3.5/Record.ts
@@ -0,0 +1,21 @@
+import * as R from '../../src/Record'
+
+declare const dictionaryString: { [key: string]: number }
+declare const recordString: Record<string, number>
+declare const recordStringEnum: Record<'a' | 'b', number>
+
+declare const keyString: string
+
+//
+// hasOwnProperty
+//
+
+if (R.hasOwnProperty(keyString, dictionaryString)) {
+  keyString // $ExpectType string
+}
+if (R.hasOwnProperty(keyString, recordString)) {
+  keyString // $ExpectType string
+}
+if (R.hasOwnProperty(keyString, recordStringEnum)) {
+  keyString // $ExpectType "a" | "b"
+}
diff --git a/src/Record.ts b/src/Record.ts
@@ -123,7 +123,7 @@ export function toUnfoldable<F>(unfoldable: Unfoldable<F>): <A>(r: Record<string
 }
 
 /**
- * Insert or replace a key/value pair in a map
+ * Insert or replace a key/value pair in a record
  *
  * @since 2.0.0
  */
@@ -144,7 +144,7 @@ const _hasOwnProperty = Object.prototype.hasOwnProperty
 /**
  * @since 2.0.0
  */
-export function hasOwnProperty<K extends string>(k: K, r: Record<K, unknown>): boolean {
+export function hasOwnProperty<K extends string>(k: string, r: Record<K, unknown>): k is K {
   return _hasOwnProperty.call(r, k)
 }