Add command pattern

typescript/src/patterns/Behavioral/Command.ts

@@ -0,0 +1,60 @@
+// Higher-order function as Command
+type Command = () => void;
+
+// Concrete Commands
+const simpleCommand = (payload: string): Command => {
+    return () => {
+        console.log(`Simple Command: See, I can do simple things like printing (${payload})`);
+    };
+};
+
+const complexCommand = (receiver: Receiver, a: string, b: string): Command => {
+    return () => {
+        console.log('Complex Command: Complex stuff should be done by a receiver object.');
+        receiver.doSomething(a);
+        receiver.doSomethingElse(b);
+    };
+};
+
+// Receiver
+class Receiver {
+    doSomething(a: string): void {
+        console.log(`Receiver: Working on (${a}.)`);
+    }
+
+    doSomethingElse(b: string): void {
+        console.log(`Receiver: Also working on (${b}.)`);
+    }
+}
+
+// Invoker
+class Invoker {
+    private onStart: Command | undefined;
+    private onFinish: Command | undefined;
+
+    setOnStart(command: Command): void {
+        this.onStart = command;
+    }
+
+    setOnFinish(command: Command): void {
+        this.onFinish = command;
+    }
+
+    doSomethingImportant(): void {
+        console.log('Invoker: Does anybody want something done before I begin?');
+        this.onStart?.();
+
+        console.log('Invoker: ...doing something really important...');
+
+        console.log('Invoker: Does anybody want something done after I finish?');
+        this.onFinish?.();
+    }
+}
+
+// Client code
+const invoker = new Invoker();
+const receiver = new Receiver();
+invoker.setOnStart(simpleCommand('Say Hi!'));
+invoker.setOnFinish(complexCommand(receiver, 'Send email', 'Save report'));
+
+invoker.doSomethingImportant();