checkpoint

001.ts

@@ -1,6 +1,13 @@
 // # Types 101
 
 
+// ---
+
+// SLIDE
+
+// ---
+
+
 // ## JS Primitives
 
 let _number: number = 1;
@@ -13,6 +20,13 @@ let _undefined: undefined = undefined;
 let _null: null = null;
 
 
+// ---
+
+// SLIDE
+
+// ---
+
+
 // ## Objects
 
 let _obj1: object = { a: 'value' }; // don't, any non primitive
@@ -25,6 +39,13 @@ type UnknownObject = Record<string, unknown>;
 let _obj6: UnknownObject = { a: 'value' };
 
 
+// ---
+
+// SLIDE
+
+// ---
+
+
 // ## Functions
 
 let _fun1: Function = (x) => x++; // don't
@@ -41,6 +62,13 @@ let _callableFun5 = _fun5 as Function;
 _callableFun5();
 
 
+// ---
+
+// SLIDE
+
+// ---
+
+
 // ## Any, unknown, never
 
 function getA1(obj: any) {
@@ -67,6 +95,13 @@ function throwError(msg: string): never {
 }
 
 
+// ---
+
+// SLIDE
+
+// ---
+
+
 // ## Literals
 
 let _true: true = true;
@@ -82,6 +117,13 @@ type HttpVerbs = LowercaseHttpVerbs | Uppercase<LowercaseHttpVerbs>;
 // see: Uppercase, Lowercase, Capitalize, Uncapitalize
 
 
+// ---
+
+// SLIDE
+
+// ---
+
+
 // ## Arrays and tuples
 
 let _strArr1: string[] = ['val1', 'val2'];
@@ -95,4 +137,12 @@ let _tuple2: [string, number, string] = ['val1', 2, 'val3'];
 let _tuple3: [string, number, string?] = ['val1', 2];
 let _tuple4: [string, ...number[]] = ['val1', 2, 3, 4];
 let _tuple5: [string, ...number[], string] = ['val1', 2, 3, 4, 'val5']; // TS >= 4.2
-let _tuple6: [first: string, second: string] = ['val1', 'val2'];
+let _tuple6: [first: string, second: string] = ['val1', 'val2'];
+
+
+// ---
+
+// NEXT
+
+// ---
+

002.ts

@@ -1,6 +1,13 @@
 // # Unions and Intersections
 
 
+// ---
+
+// SLIDE
+
+// ---
+
+
 // ## Basic example
 
 type SingleDigitPrime = 2 | 3 | 5 | 7;
@@ -13,6 +20,13 @@ type SingleDigitPrimeAndOdd = SingleDigitPrime & SingleDigitOdd;
 // result: 3 | 5 | 7
 
 
+// ---
+
+// SLIDE
+
+// ---
+
+
 // ## Object union
 
 // Basically an or operator
@@ -39,7 +53,14 @@ function payTaxes(entity: Human | Company): void {
 }
 
 
-// # Object intersection
+// ---
+
+// SLIDE
+
+// ---
+
+
+// ## Object intersection
 
 interface DbModel { id: number; }
 type ChildObject = { parentId: number; };
@@ -54,6 +75,13 @@ function addChild(parentId: number, child: DbModel): ChildDbModel {
 }
 
 
+// ---
+
+// SLIDE
+
+// ---
+
+
 // ## Narrowing down types with intersections
 
 type Bipedal = { usesFourLegs: false; usesTwoLegs: true; };
@@ -84,6 +112,13 @@ const chicken: Bird = {
 };
 
 
+// ---
+
+// SLIDE
+
+// ---
+
+
 // ## Side note: optional is not the same as undefined
 
 let _obj7: { a?: string } = {};
@@ -92,6 +127,13 @@ let _obj7: { a?: string } = {};
 // result: Property 'a' is missing in type '{}' but required in type '{ a: string | undefined; }'.ts(2741)
 
 
+// ---
+
+// SLIDE
+
+// ---
+
+
 // ## interface extends
 
 // Basically the same as object intersections
@@ -109,6 +151,13 @@ const chicken2: Bird2 = chicken;
 // result: An interface can only extend an object type or intersection of object types with statically known members.ts(2312)
 
 
+// ---
+
+// SLIDE
+
+// ---
+
+
 // ## A "real" union of objects
 
 // Goal: shared types are required and individual ones are optional
@@ -123,6 +172,13 @@ function payTaxes2(entity: LegalEntity): void {
 }
 
 
+// ---
+
+// SLIDE
+
+// ---
+
+
 // ## Side note: JS nullish coalescing && optional chaining
 
 function old_getChildId(parent: any): number | null {
@@ -139,3 +195,81 @@ function new_getChildId(parent: any): number | null {
 
 globalThis.notSureIfThisFunctionExists?.();
 
+
+// ---
+
+// SLIDE
+
+// ---
+
+
+// ## Function overloads
+
+function len(s: string): number;
+function len(arr: any[]): number;
+
+function len(x: string | any[]) {
+    return x.length;
+}
+
+len('string');
+len([1, 2, 3]);
+
+
+// ---
+
+// SLIDE
+
+// ---
+
+
+// ## Overloading arrow functions
+
+type Len2 = {
+    (s: string): number;
+    (arr: any[]): number;
+}
+let len2: Len2 = (x: string | any[]) => x.length;
+
+len2('string');
+len2([1, 2, 3]);
+
+
+// ---
+
+// SLIDE
+
+// ---
+
+
+// ## Overloading arrow functions v2
+
+type Len3 = ((s: string) => number) & ((arr: any[]) => number);
+let len3: Len3 = (x: string | any[]) => x.length;
+
+len3('string');
+len3([1, 2, 3]);
+
+
+// ---
+
+// SLIDE
+
+// ---
+
+
+// ## Side note: If you ever need to type `this`
+
+function socketController(this: SocketControllerContext, socket: any, data: any, ack?: () => void) {
+    const activeConnection = this.activeConnectionsRepository.findBySocket(socket);
+    // ...
+}
+
+type SocketControllerContext = { activeConnectionsRepository: { findBySocket(socket: any): any }; };
+
+
+// ---
+
+// NEXT
+
+// ---