Convert cpu6502 to Typescript

js/types.ts

@@ -16,3 +16,28 @@ export type word = number;
 export type address = word;
 
 export type memory = Uint8Array | byte[];
+
+export interface Memory {
+  /** Read a byte. */
+  read(page: byte, offset: byte): byte;
+  /** Write a byte. */
+  write(page: byte, offset: byte, value: byte): void;
+}
+
+/** A mapped region of memory. */
+export interface MemoryPages extends Memory {
+  /** Start page. */
+  start(): byte;
+  /** End page, inclusive. */
+  end(): byte;
+}
+
+/**
+ * Extracts the members of a constant array as a type. Used as:
+ *
+ * @example
+ * const SOME_VALUES = ['a', 'b', 1, 2] as const;
+ * type SomeValues = MemberOf<typeof SOME_VALUES>; // 'a' | 'b' | 1 | 2
+ */
+export type MemberOf<T extends ReadonlyArray<unknown>> =
+  T extends ReadonlyArray<infer E> ? E : never;