Typeguard in TS

Author: Akash52

typescript-masterclass/README.md

@@ -264,3 +264,32 @@ const item: Record<keyof TrackStates, string> = {
 //Number are coerced to string
 dictionary[0] = item;
 ```
+
+### Typeguard in TS
+
+```ts
+class Song {
+  constructor(public title: string, public duration: string | number) {}
+}
+
+function getSongDuration(item: Song) {
+  if (typeof item.duration === "string") {
+    return item.duration;
+  }
+  const { duration } = item;
+  const minutes = Math.floor(duration / 60000);
+  const seconds = (duration / 1000) % 60;
+  return `${minutes}:${seconds}`;
+}
+
+const songDurationFromString = getSongDuration(
+  new Song("Wonderful Wonderful", "05:30")
+);
+console.log(songDurationFromString);
+
+const songDurationFromMS = getSongDuration(
+  new Song("Wonderful Wonderful", 330000)
+);
+
+console.log(songDurationFromMS);
+```

typescript-masterclass/src/app.ts

@@ -1,14 +1,24 @@
-let dictionary: Record<string, TrackStates> = {};
+class Song {
+  constructor(public title: string, public duration: string | number) {}
+}
 
-interface TrackStates {
-  current: string;
-  next: string;
+function getSongDuration(item: Song) {
+  if (typeof item.duration === "string") {
+    return item.duration;
+  }
+  const { duration } = item;
+  const minutes = Math.floor(duration / 60000);
+  const seconds = (duration / 1000) % 60;
+  return `${minutes}:${seconds}`;
 }
 
-const item: Record<keyof TrackStates, string> = {
-  current: "abc23ds",
-  next: "dsfsdflink3",
-};
+const songDurationFromString = getSongDuration(
+  new Song("Wonderful Wonderful", "05:30")
+);
+console.log(songDurationFromString);
+
+const songDurationFromMS = getSongDuration(
+  new Song("Wonderful Wonderful", 330000)
+);
 
-//Number are coerced to string
-dictionary[0] = item;
+console.log(songDurationFromMS);