add more typescript examples

07-type-mapping/main.ts

@@ -1,34 +1,36 @@
 enum OpCode {
-    PING,
-    HELLO,
-    MOVE,
+  PING,
+  HELLO,
+  MOVE,
 }
 
+type PingEvent = Record<string, never>;
+
 type HelloEvent = {
-    name: string;
+  name: string;
 };
 
 type MoveEvent = {
-    x: number;
-    y: number;
+  x: number;
+  y: number;
 };
 
 type OpArgsMapping = {
-    [OpCode.PING]: null;
-    [OpCode.HELLO]: HelloEvent;
-    [OpCode.MOVE]: MoveEvent;
+  [OpCode.PING]: PingEvent;
+  [OpCode.HELLO]: HelloEvent;
+  [OpCode.MOVE]: MoveEvent;
 };
 
 class WebSocketClient {
-    public op<TOp extends OpCode, TArgs extends OpArgsMapping[TOp]>(
-        op: TOp,
-        args: TArgs,
-    ) {
-        // ...
-    }
+  public op<TOp extends OpCode, TArgs extends OpArgsMapping[TOp]>(
+    op: TOp,
+    args: TArgs,
+  ) {
+    // ...
+  }
 }
 
-function main() {
-    const client = new WebSocketClient();
-    client.op(OpCode.HELLO, { name: "foo" });
+function main_ws() {
+  const client = new WebSocketClient();
+  client.op(OpCode.PING, {});
 }

08-type-programming/main.ts

@@ -0,0 +1,23 @@
+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("/hello", {});
+  navigate("/hello/{name}", { name: "foo" });
+}

README.md

@@ -0,0 +1,8 @@
+# Type Level Programming
+
+## Sources
+
+- https://www.emoses.org/posts/resolver-resolved-pattern/
+- https://farazdagi.com/posts/2024-04-07-typestate-pattern/
+- https://youtu.be/_ccDqRTx-JU
+- https://type-level-typescript.com/