fix: better support optional nested types

Author: RossWilliams

src/caseConvert.ts

@@ -96,21 +96,23 @@ export type ToCamel<S extends string | number | symbol> = S extends string
   : never;
 
 // eslint-disable-next-line @typescript-eslint/ban-types
-export type ObjectToCamel<T extends object> = {
-  // eslint-disable-next-line @typescript-eslint/ban-types
-  [K in keyof T as ToCamel<K>]: T[K] extends Array<unknown>
-    ? // eslint-disable-next-line @typescript-eslint/ban-types
-      T[K] extends Array<infer ArrayType>
-      ? // eslint-disable-next-line @typescript-eslint/ban-types
-        ArrayType extends object
-        ? Array<ObjectToCamel<ArrayType>>
-        : T[K]
-      : never
-    : // eslint-disable-next-line @typescript-eslint/ban-types
-    T[K] extends object
-    ? ObjectToCamel<T[K]>
-    : T[K];
-};
+export type ObjectToCamel<T extends object | undefined> = T extends undefined
+  ? undefined
+  : {
+      // eslint-disable-next-line @typescript-eslint/ban-types
+      [K in keyof T as ToCamel<K>]: T[K] extends Array<unknown>
+        ? // eslint-disable-next-line @typescript-eslint/ban-types
+          T[K] extends Array<infer ArrayType>
+          ? // eslint-disable-next-line @typescript-eslint/ban-types
+            ArrayType extends object
+            ? Array<ObjectToCamel<ArrayType>>
+            : T[K]
+          : never
+        : // eslint-disable-next-line @typescript-eslint/ban-types
+        T[K] extends object | undefined
+        ? ObjectToCamel<T[K]>
+        : T[K];
+    };
 
 export type ToSnake<S extends string | number | symbol> = S extends string
   ? S extends CapitalChars
@@ -153,20 +155,24 @@ export type ToSnake<S extends string | number | symbol> = S extends string
   : never;
 
 // eslint-disable-next-line @typescript-eslint/ban-types
-export type ObjectToSnake<T extends object> = {
-  [K in keyof T as ToSnake<K>]: T[K] extends Array<unknown>
-    ? // eslint-disable-next-line @typescript-eslint/ban-types
-      T[K] extends Array<infer ArrayType>
-      ? // eslint-disable-next-line @typescript-eslint/ban-types
-        ArrayType extends object
-        ? Array<ObjectToSnake<ArrayType>>
-        : T[K]
-      : never
-    : // eslint-disable-next-line @typescript-eslint/ban-types
-    T[K] extends object
-    ? ObjectToSnake<T[K]>
-    : T[K];
-};
+export type ObjectToSnake<T extends object | undefined> = T extends undefined
+  ? undefined
+  : {
+      [K in keyof T as ToSnake<K>]: T[K] extends Array<unknown>
+        ? // eslint-disable-next-line @typescript-eslint/ban-types
+          T[K] extends Array<infer ArrayType>
+          ? // eslint-disable-next-line @typescript-eslint/ban-types
+            ArrayType extends object
+            ? Array<ObjectToSnake<ArrayType>>
+            : T[K]
+          : never
+        : // eslint-disable-next-line @typescript-eslint/ban-types
+        T[K] extends object | undefined
+        ? ObjectToSnake<T[K]>
+        : //  Exclude<T[K], undefined> extends object
+          //  ? ObjectToSnake<Exclude<T[K], undefined>>
+          T[K];
+    };
 
 type CapitalLetters =
   | 'A'

test/caseConvert.test.ts

@@ -5,6 +5,7 @@ import {
   ToCamel,
   ToSnake,
   toCamel,
+  ObjectToSnake,
 } from '../src/caseConvert';
 
 describe('Property name converter', () => {
@@ -19,6 +20,9 @@ describe('Property name converter', () => {
       an_object: {
         a_1: 'a1',
         a_2: 'a2',
+        a_3: {
+          b_4: 'b4',
+        },
       },
     });
 
@@ -33,6 +37,7 @@ describe('Property name converter', () => {
     expect(testToCamel.anArrayOfObjects[0].aC).toEqual('ac');
     expect(testToCamel.anObject.a1).toEqual('a1');
     expect(testToCamel.anObject.a2).toEqual('a2');
+    expect(testToCamel.anObject.a3.b4).toEqual('b4');
   });
 
   it('converts to snake_case', () => {
@@ -46,6 +51,9 @@ describe('Property name converter', () => {
       anObject: {
         A1: 'a_1',
         A2: 'a_2',
+        A3: {
+          B4: 'b_4',
+        },
       },
     });
 
@@ -60,6 +68,7 @@ describe('Property name converter', () => {
     expect(testToSnake.an_array_of_objects[0].a_c).toEqual('ac');
     expect(testToSnake.an_object.a1).toEqual('a_1');
     expect(testToSnake.an_object.a2).toEqual('a_2');
+    expect(testToSnake.an_object.a3.b4).toEqual('b_4');
   });
 });
 
@@ -181,3 +190,37 @@ type T22 = ToSnake<'abc25D50'>;
 const _s22: AssertEqual<T22, 'abc_25_d50'> = true;
 type T23 = ToSnake<'abc25A50'>;
 const _s23: AssertEqual<T23, 'abc_25_a50'> = true;
+
+interface I24 {
+  optionalObject?: {
+    aProp: string;
+    bProp:
+      | {
+          cProp: string;
+        }
+      | undefined;
+  };
+}
+
+interface I242 {
+  optional_object?: {
+    a_prop: string;
+    b_prop:
+      | {
+          c_prop: string;
+        }
+      | undefined;
+  };
+}
+
+const _c24: I24 = {
+  optionalObject: {
+    aProp: 'a',
+    bProp: {
+      cProp: 'c',
+    },
+  },
+};
+const _c242: I242 = objectToSnake(_c24);
+
+const _s24: AssertEqual<I242, ObjectToSnake<I24>> = true;