M-Bekheet · January 12, 2023 20:00 · Jan 12, 2023 · Jan 12, 2023
diff --git a/Generics.ts b/Generics.ts
@@ -44,7 +44,7 @@ set.add(1);
 
 const addIdToObject = <T>(obj: T) => ({ ...obj, id: 3 });
 
-const student = addIdToObject({ name: "Mahmoud", age: 26 });
+const student = addIdToObject({ name: "Jack", age: 32 });
 
 /*
 *

diff --git a/Generics.ts b/Generics.ts
@@ -0,0 +1,126 @@
+// Generics
+
+/*
+*
+  ===> Ex1
+*  
+*/
+
+type G1<S> = {
+  data: S;
+};
+
+type E1 = G1<string>;
+type E2 = G1<{ firstName: string }>;
+
+/*
+*
+  ===> Ex2: With Functions
+*  
+*/
+
+const makeFetch = <TData>(url: string): Promise<TData> =>
+  fetch(url).then((res) => res.json());
+
+const students = makeFetch<string[]>("/students");
+const count = makeFetch<{ count: number }>("/count");
+
+/*
+*
+  ===> Ex3: You can use generics with JS Set
+*  
+*/
+
+const set = new Set<number>();
+
+set.add(1);
+// set.add("text") //error
+
+/*
+*
+  ===> Ex4: Inferring types (notice the addition of the id type)
+*  
+*/
+
+const addIdToObject = <T>(obj: T) => ({ ...obj, id: 3 });
+
+const student = addIdToObject({ name: "Mahmoud", age: 26 });
+
+/*
+*
+  ===> Ex5: ReturnType & Awaited
+*  
+*/
+
+//we extends a function as ReturnType only works on functions so we tell TS that T type is a function
+type Result<T extends (...args: any) => any> = ReturnType<T>;
+type Res = Result<() => "Hello">;
+
+type Result2<T> = Awaited<Promise<T>>;
+type Res2 = Result2<number>;
+
+//both together
+type GetPromiseReturnType<T extends (...args: any) => any> = Awaited<
+  ReturnType<T>
+>;
+
+type Result3 = GetPromiseReturnType<() => Promise<{ firstName: string }>>;
+
+/*
+*
+  ===> Ex6: Add function constraint
+*  
+*/
+
+// Record: set object with constraint types (string, number, ...)
+const getHighestValue = <TObj extends Record<string, number>>(
+  obj: TObj
+): {
+  key: keyof TObj;
+  value: number;
+} => {
+  const keys = Object.keys(obj);
+  let key = keys[0];
+  let highest = obj[keys[0]];
+
+  for (const item of keys) {
+    if (obj[item] > highest) {
+      highest = obj[item];
+      key = item;
+    }
+  }
+
+  return { key, value: highest };
+};
+
+const pair = getHighestValue({
+  a: 1,
+  b: 2,
+  c: 3,
+  // d: false /==> error
+});
+
+/*
+*
+  ===> Ex7: constraint a return type to a specific key of enumerable
+*  
+*/
+
+const getValue = <TObj, TKey extends keyof TObj>(obj: TObj, key: TKey) => {
+  return obj[key];
+};
+
+const val = getValue({ a: 1, b: true, c: "text" }, "c");
+
+/*
+*
+  ===> Ex8: defaults in type arguments
+*  
+*/
+
+const createSet = <T = string>() => new Set<T>();
+const set1 = createSet<number>();
+const set2 = createSet<[]>();
+const set3 = createSet(); // using the default string argument
+
+export {};