add more typescript examples

07-type-mapping/main.ts

@@ -4,6 +4,8 @@ enum OpCode {
   MOVE,
 }
 
+type PingEvent = Record<string, never>;
+
 type HelloEvent = {
   name: string;
 };
@@ -14,7 +16,7 @@ type MoveEvent = {
 };
 
 type OpArgsMapping = {
-  [OpCode.PING]: {};
+  [OpCode.PING]: PingEvent;
   [OpCode.HELLO]: HelloEvent;
   [OpCode.MOVE]: MoveEvent;
 };

08-type-programming/main.ts

@@ -1,13 +1,23 @@
-type ParseUrlParams<Url> = Url extends `${infer Start}/${infer Rest}`
-  ? ParseUrlParams<Start> & ParseUrlParams<Rest>
+type ParseUrlParamsRaw<Url> = Url extends `${infer Start}/${infer Rest}`
+  ? ParseUrlParamsRaw<Start> & ParseUrlParamsRaw<Rest>
   : Url extends `{${infer Param}}`
     ? { [P in Param]: string }
     : {};
 
+// ParseUrlParamsRaw allows passing objects with any keys (i.e. `{name: "foo"}`) even though
+// an empty object is expected (`{}`). This type constraint enforces this by checking if
+// the result of ParseUrlParamsRaw<Url> is `{}`. `keyof {}` evaluates to `never`, so
+// when `{}` is evaluated an empty Record is expected, otherwise the result of
+// ParseUrlParamsRaw is expected.
+type ParseUrlParams<Url> = keyof ParseUrlParamsRaw<Url> extends never
+  ? Record<string, never>
+  : ParseUrlParamsRaw<Url>;
+
 function navigate<P extends string>(path: P, params: ParseUrlParams<P>) {
   // ...
 }
 
 function main() {
-  navigate("/foo/bar", { foo: "asd" });
+  navigate("/hello", {});
+  navigate("/hello/{name}", { name: "foo" });
 }