🤖 Merge PR #70966 [lodash] enhance _.capitalize to return a capitalized string type by @Ha-limLee

Ha-limLee · web-flow · commit 48981c282cb1 · 2024-10-29T17:15:48.000-07:00
diff --git a/types/lodash/common/lang.d.ts b/types/lodash/common/lang.d.ts
@@ -1,5 +1,5 @@
 import _ = require("../index");
-// eslint-disable-next-line @definitelytyped/strict-export-declare-modifiers
+// eslint-disable-next-line @definitelytyped/strict-export-declare-modifiers, @typescript-eslint/no-unsafe-function-type
 type GlobalFunction = Function;
 declare module "../index" {
     type FunctionBase = GlobalFunction;
diff --git a/types/lodash/common/string.d.ts b/types/lodash/common/string.d.ts
@@ -29,19 +29,19 @@ declare module "../index" {
          * @param string The string to capitalize.
          * @return Returns the capitalized string.
          */
-        capitalize(string?: string): string;
+        capitalize<T extends string>(string?: T): Capitalize<Lowercase<T>>;
     }
     interface LoDashImplicitWrapper<TValue> {
         /**
          * @see _.capitalize
          */
-        capitalize(): string;
+        capitalize(): Capitalize<Lowercase<TValue extends string ? TValue : never>>;
     }
     interface LoDashExplicitWrapper<TValue> {
         /**
          * @see _.capitalize
          */
-        capitalize(): StringChain;
+        capitalize(): StringChain<Capitalize<Lowercase<TValue extends string ? TValue : never>>>;
     }
 
     interface LoDashStatic {
diff --git a/types/lodash/fp.d.ts b/types/lodash/fp.d.ts
@@ -240,7 +240,7 @@ declare namespace _ {
     type LodashBindKey1x1 = (key: string) => (...args: any[]) => any;
     type LodashBindKey1x2 = (object: object) => (...args: any[]) => any;
     type LodashCamelCase = (string: string) => string;
-    type LodashCapitalize = (string: string) => string;
+    type LodashCapitalize = <T extends string>(string: T) => Capitalize<Lowercase<T>>;
     type LodashCastArray = <T>(value: lodash.Many<T>) => T[];
     type LodashCeil = (n: number) => number;
     interface LodashChunk {
diff --git a/types/lodash/lodash-tests.ts b/types/lodash/lodash-tests.ts
@@ -6623,10 +6623,27 @@ fp.now(); // $ExpectType number
 
 // _.capitalize
 {
-    _.capitalize("fred"); // $ExpectType string
-    _("fred").capitalize(); // $ExpectType string
-    _.chain("fred").capitalize(); // $ExpectType StringChain<string>
-    fp.capitalize("fred"); // $ExpectType string
+    _.capitalize("fred"); // $ExpectType "Fred"
+    _.capitalize("FRED"); // $ExpectType "Fred"
+    _.capitalize("fred" as string); // $ExpectType Capitalize<Lowercase<string>>
+    // @ts-expect-error cannot assign non string type
+    _.capitalize(123);
+
+    _("fred").capitalize(); // $ExpectType "Fred"
+    _("FRED").capitalize(); // $ExpectType "Fred"
+    _("fred" as string).capitalize(); // $ExpectType Capitalize<Lowercase<string>>
+    _(123).capitalize(); // $ExpectType never
+
+    _.chain("fred").capitalize(); // $ExpectType StringChain<"Fred">
+    _.chain("FRED").capitalize(); // $ExpectType StringChain<"Fred">
+    _.chain("fred" as string).capitalize(); // $ExpectType StringChain<Capitalize<Lowercase<string>>>
+    _.chain(123).capitalize(); // $ExpectType StringChain<never>
+
+    fp.capitalize("fred"); // $ExpectType "Fred"
+    fp.capitalize("FRED"); // $ExpectType "Fred"
+    fp.capitalize("fred" as string); // $ExpectType Capitalize<Lowercase<string>>
+    // @ts-expect-error cannot assign non string type
+    fp.capitalize(123);
 }
 
 // _.deburr
