Use async/await instead of setTimeout

Author: tzeikob

behavioral/observer/readme.md

@@ -61,6 +61,8 @@ class Observable {
 
 > We could call the listener with `this` instead of `null` in case we need to have access the observable within the listener's code via the `this` operator.
 
+Bear in mind that this method should always be called from an asynchronous context, for instance an operation of the observable running asynchronously.
+
 ### An observable must have a purpose
 
 An observable must have a purpose, it must provide at least one asynchronous `operation`. It doesn't have to be an asynchronous operation, even though it only makes sense to have an asynchronous observable. Within each operation the observable must use the `emit` method in order to call every listener given this event type along with any data arguments.
@@ -69,21 +71,19 @@ An observable must have a purpose, it must provide at least one asynchronous `op
 class Observable {
   ...
 
-  operation () {
-    setTimeout(() => {
-      // Execute any business logic
-      const valueA = ...
-      const valueB = ...
-      ...
-
-      // Emit the success of the operation
-      this.emit("success", valueA, valueB, ...);
-    });
+  async operation () {
+    // Execute any business logic
+    const valueA = await ...
+    const valueB = await ...
+    ...
+    
+    // Emit the success of the operation
+    this.emit("success", valueA, valueB, ...);
   }
 }
 ```
 
-> We are using the `setTimeout` function to mimic the execution of an asynchronous operation.
+> Operation is set to be an async function in order to call operations asynchronously.
 
 ### Register event listeners
 
@@ -106,20 +106,18 @@ A special care must be taken regarding the error handling in the observer patter
 class Observable {
   ...
 
-  operation () {
-    setTimeout(() => {
-      try {
-        // Execute any business logic
-        const valueA = ...
-        const valueB = ...
-        ...
-
-        // Emit the success of the operation
-        this.emit("success", valueA, valueB, ...);
-      } catch (error) {
-        this.emit("error", error); // Emit the thrown error
-      }
-    });
+  async operation () {
+    try {
+      // Execute any business logic
+      const valueA = await ...
+      const valueB = await ...
+      ...
+
+      // Emit the success of the operation
+      this.emit("success", valueA, valueB, ...);
+    } catch (error) {
+      this.emit("error", error); // Emit the thrown error
+    }
   }
 }
 ```
@@ -161,20 +159,18 @@ class Observable {
     }
   }
 
-  operation () {
-    setTimeout(() => {
-      try {
-        // Execute any business logic
-        const valueA = ...
-        const valueB = ...
-        ...
-
-        // Emit the success of the operation
-        this.emit("success", valueA, valueB, ...);
-      } catch (error) {
-        this.emit("error", error); // Emit the thrown error
-      }
-    });
+  async operation () {
+    try {
+      // Execute any business logic
+      const valueA = await ...
+      const valueB = await ...
+      ...
+
+      // Emit the success of the operation
+      this.emit("success", valueA, valueB, ...);
+    } catch (error) {
+      this.emit("error", error); // Emit the thrown error
+    }
   }
 }
 

behavioral/observer/thermometer.js

@@ -1,5 +1,8 @@
+import { sensors } from "iot";
+
 class Thermometer {
   constructor() {
+    this.running = false;
     this.previous = 0;
     this.temperature = 0;
 
@@ -30,11 +33,13 @@ class Thermometer {
     }
   }
 
-  update (value) {
-    setTimeout(() => {
+  async start () {
+    this.running = true;
+
+    while (this.running) {
       try {
         this.previous = this.temperature;
-        this.temperature = value;
+        this.temperature = await sensors.readTemperature();
 
         const delta = this.temperature - this.previous;
 
@@ -46,7 +51,11 @@ class Thermometer {
       } catch (error) {
         this.emit("error", error);
       }
-    });
+    }
+  }
+
+  stop () {
+    this.running = false;
   }
 
   removeListener (event, listener) {
@@ -61,34 +70,22 @@ class Thermometer {
 
 const t = new Thermometer();
 
-t.update(10);
+t.start();
 
 t.on("increase", (temp, delta) => {
-  console.log(`Temperature increased up to ${temp} with a delta ${delta}`)
+  console.log({ temp, delta });
 });
 
 t.on("decrease", (temp, delta) => {
-  console.log(`Temperature decreased to ${temp} with a delta ${delta}`)
+  console.log({ temp, delta });
 });
 
 t.on("error", (error) => {
-  console.error(`An error occurred updating the temperature: ${error.message}`)
+  console.error(`Error: ${error.message}`)
 });
 
-t.on("increase", (temp, delta) => {
-  console.log(`With the temperature increased by ${delta} is getting warmer`)
-});
-
-t.update(-15);
-t.update(8);
-t.update(8);
-t.update(40);
-
 // Async output:
-// Temperature increased up to 10 with a delta 10
-// With the temperature increased by 10 is getting warmer
-// Temperature decreased to -15 with a delta -25
-// Temperature increased up to 8 with a delta 23
-// With the temperature increased by 23 is getting warmer
-// Temperature increased up to 40 with a delta 32
-// With the temperature increased by 32 is getting warmer
+// { temp: -1, delta: -1 }
+// { temp: -3, delta: -2 }
+// { temp: -5, delta: -2 }
+// { temp: -7, delta: -2 }