instanceof typeguard in ts

Author: Akash52

typescript-masterclass/README.md

@@ -293,3 +293,42 @@ const songDurationFromMS = getSongDuration(
 
 console.log(songDurationFromMS);
 ```
+
+### instanceof typeguard in ts
+
+```ts
+class Foo {
+  bar() {}
+}
+
+const bar = new Foo();
+
+console.log(bar);
+
+// console.log(bar instanceof Foo);
+// console.log(Object.getPrototypeOf(bar) === Foo.prototype);
+
+class Song {
+  constructor(public title: string, public duration: number) {}
+}
+
+class Playlist {
+  constructor(public name: string, public songs: Song[]) {}
+}
+
+function getItemName(item: Song | Playlist) {
+  if (item instanceof Song) {
+    return item.title;
+  }
+  return item.name;
+}
+
+const songName = getItemName(new Song("wonderful wonderful", 300000));
+console.log("Song Name :", songName);
+
+const playlistName = getItemName(
+  new Playlist("The Best Songs", [new Song("The Man", 30000)])
+);
+
+console.log("Playlist Name :", playlistName);
+```

typescript-masterclass/src/app.ts

@@ -1,24 +1,34 @@
+class Foo {
+  bar() {}
+}
+
+const bar = new Foo();
+
+console.log(bar);
+
+// console.log(bar instanceof Foo);
+// console.log(Object.getPrototypeOf(bar) === Foo.prototype);
+
 class Song {
-  constructor(public title: string, public duration: string | number) {}
+  constructor(public title: string, public duration: number) {}
+}
+
+class Playlist {
+  constructor(public name: string, public songs: Song[]) {}
 }
 
-function getSongDuration(item: Song) {
-  if (typeof item.duration === "string") {
-    return item.duration;
+function getItemName(item: Song | Playlist) {
+  if (item instanceof Song) {
+    return item.title;
   }
-  const { duration } = item;
-  const minutes = Math.floor(duration / 60000);
-  const seconds = (duration / 1000) % 60;
-  return `${minutes}:${seconds}`;
+  return item.name;
 }
 
-const songDurationFromString = getSongDuration(
-  new Song("Wonderful Wonderful", "05:30")
-);
-console.log(songDurationFromString);
+const songName = getItemName(new Song("wonderful wonderful", 300000));
+console.log("Song Name :", songName);
 
-const songDurationFromMS = getSongDuration(
-  new Song("Wonderful Wonderful", 330000)
+const playlistName = getItemName(
+  new Playlist("The Best Songs", [new Song("The Man", 30000)])
 );
 
-console.log(songDurationFromMS);
+console.log("Playlist Name :", playlistName);