My feature

packages/notes-ts-fundamentals-v4/src/03-variables-and-values.ts

@@ -1,69 +1,59 @@
 //* Variable Declarations & Inference
 let temperature = 6 //! inference
-/*
-// temperature = "warm"  //! type-checking
+
+temperature = 'warm' //! type-checking
 // const humidity = 79  //! literal type
 
 //* A type as a set of allowed values
-/*
-// temperature = 23 //✔️ (1)  - re-assignability of a let
-// temperature = humidity; //! (2) - type-checking
-// humidity = temperature; //! (3) - number is not of type `79`
-// humidity = 79; //✔️ (4) - 79 is of type `79`
-// humidity = 78; //! (5) - 78 is not of type `79`
-
-
-/*
-// let temp2 = 19; //! temp2's type is { all numbers }
-// let humid2 = 79 as const; //! humidity's type is { 79 }
-// temp2 = 23; //! Is each member in { 23 } also in { all numbers }?
-// temp2 = humid2; //! Is each member in { 79 } also in { all numbers }?
-// humid2 = temp2; //! Is each member in { all numbers } also in { 79 }?
-// humid2 = 79; //! Is each member in { 79 } also in { 79 }
-// humid2 = 78; //! Is each member in { 78 } also in { 79 }
+
+temperature = 23 //✔️ (1)  - re-assignability of a let
+temperature = humidity //! (2) - type-checking
+humidity = temperature //! (3) - number is not of type `79`
+humidity = 79 //✔️ (4) - 79 is of type `79`
+humidity = 78 //! (5) - 78 is not of type `79`
+
+let temp2 = 19 //! temp2's type is { all numbers }
+let humid2 = 79 as const //! humidity's type is { 79 }
+temp2 = 23 //! Is each member in { 23 } also in { all numbers }?
+temp2 = humid2 //! Is each member in { 79 } also in { all numbers }?
+humid2 = temp2 //! Is each member in { all numbers } also in { 79 }?
+humid2 = 79 //! Is each member in { 79 } also in { 79 }
+humid2 = 78 //! Is each member in { 78 } also in { 79 }
 
 //* Implicit `any` and type annotations
-/*
-// between 500 and 1000
-// export const RANDOM_WAIT_TIME =
-//     Math.round(Math.random() * 500) + 500
 
-// let startTime = new Date()
-// let endTime
+// between 500 and 1000
+export const RANDOM_WAIT_TIME = Math.round(Math.random() * 500) + 500
 
-// setTimeout(() => {
-//     endTime = 0
-//     endTime = new Date()
-// }, RANDOM_WAIT_TIME)
+let startTime = new Date()
+let endTime: Date
 
+setTimeout(() => {
+  //   endTime = 0 //! Type 'number' is not assignable to type 'Date'
+  endTime = new Date()
+}, RANDOM_WAIT_TIME)
 
 //* Type Casting
-/*
-// let frontEndMastersFounding = new Date("Jan 1, 2012")
-// let date1 = frontEndMastersFounding
-// let date2 = frontEndMastersFounding as any;
-
-/*
-// const humid3 = 79 as number; //✔️ is 79 a number? If so, this is safe!
 
+let frontEndMastersFounding = new Date('Jan 1, 2012')
+let date1 = frontEndMastersFounding
+let date2 = frontEndMastersFounding as any
 
-/*
-// let date3 = "oops" as any as Date //! TypeScript thinks this is a Date now, but it's really a string
-// date3.toISOString() //! what do we think will happen when we run this? 💥
+const humid3 = 79 as number //✔️ is 79 a number? If so, this is safe!
 
-/*
-// let date4 = "oops" as Date
+let date3 = 'oops' as unknown as Date //! TypeScript thinks this is a Date now, but it's really a string
+date3.toISOString() //! what do we think will happen when we run this? 💥
 
+let date4 = 'oops' as Date //! TypeScript thinks this is a Date now, but it's really a string
 
 //! Function arguments and return values
 
+function add(a: number, b: number): number {
+  return a + b // strings? numbers? a mix?
+}
 
-// function add(a, b) {
-//   return a + b // strings? numbers? a mix?
-// }
-
-// const result = add(3, "4")
-// const p = new Promise(result);
+const result = add(3, 4)
+const p = new Promise(result)
 
 /**/
 

packages/notes-ts-fundamentals-v4/src/04-objects-arrays-and-tuples.ts

@@ -1,130 +1,154 @@
 //* Objects
 
+const myCar = {
+  make: 'Toyota',
+  model: 'Corolla',
+  year: 2002,
+}
+
 let car: {
   make: string
   model: string
   year: number
-}
+} = myCar
 
-/*
-//? A function that prints info about a car to stdout
-// function printCar(car: {
-//     make: string
-//     model: string
-//     year: number
-// }) {
-//     console.log(`${car.make} ${car.model} (${car.year})`)
-// }
+// ? A function that prints info about a car to stdout
+function printCar(car: {
+  make: string
+  model: string
+  year: number
+  chargeVoltage?: number
+}) {
+  let str = `${car.make} ${car.model} (${car.year})`
+  if (typeof car.chargeVoltage !== 'undefined')
+    str += `// ${car.chargeVoltage}v`
+  console.log(str)
+}
 
-// printCar(car)
+printCar(car)
 
-/*
 //* Optional properties
 //? Insert into function printCar
 // let str = `${car.make} ${car.model} (${car.year})`
 // car.chargeVoltage
-// if (typeof car.chargeVoltage !== "undefined")
-//   str += `// ${car.chargeVoltage}v`
-
-/*
-// printCar({ //? original fn works
-//     make: "Honda",
-//     model: "Accord",
-//     year: 2017,
-// })
-
-// printCar({ //? optional property works too!
-//     make: "Tesla",
-//     model: "Model 3",
-//     year: 2020,
-//     chargeVoltage: 220,
-// })
-
-/*
+
+printCar({
+  //? original fn works
+  make: 'Honda',
+  model: 'Accord',
+  year: 2017,
+})
+
+printCar({
+  //? optional property works too!
+  make: 'Tesla',
+  model: 'Model 3',
+  year: 2020,
+  chargeVoltage: 220,
+})
+
 //* Excess property checking
 
-// printCar({
-//     make: "Tesla",
-//     model: "Model 3",
-//     year: 2020,
-//     color: "RED", //? EXTRA PROPERTY
-// })
+printCar({
+  ...{
+    //? original fn works if we use spread syntax
+    make: 'Tesla',
+    model: 'Model 3',
+    year: 2020,
+    color: 'RED', //? EXTRA PROPERTY
+  },
+})
+
+// above code can also be written as:
+printCar({
+  ...{
+    make: 'Tesla',
+    model: 'Model 3',
+    year: 2020,
+  },
+  ...{ color: 'RED' },
+})
 
-/*
 //* Index signatures
 
 //? Dictionary of phone #s
-// const phones = {
-//     home: { country: "+1", area: "211", number: "652-4515" },
-//     work: { country: "+1", area: "670", number: "752-5856" },
-//     fax: { country: "+1", area: "322", number: "525-4357" },
-// }
-/*
-//? Model as an index signature
-// const phones: {
-//     [k: string]: {
-//         country: string
-//         area: string
-//         number: string
-//     }
-// } = {}
+const phones: {
+  mobile: {
+    country: string
+    area: string
+    number: string
+  }
+  [k: string]: {
+    country: string
+    area: string
+    number: string
+  }
+} = {
+  home: { country: '+1', area: '211', number: '652-4515' },
+  work: { country: '+1', area: '670', number: '752-5856' },
+  mobile: { country: '+1', area: '322', number: '525-4357' },
+}
+
+console.log(phones.home.country)
+console.log(phones.work)
+console.log(phones.fax) //! undefined, but no error!
+console.log(phones.mobile) //! still works, even though we have an index signature!
 
 //*  Array Types
 
-/*
-// const fileExtensions = ["js", "ts"]
+const fileExtensions = ['js', 'ts']
 //        ^? string[]
 
-// const cars = [ //? Let's look at an array of objects
-//     {
-//         make: "Toyota",
-//         model: "Corolla",
-//         year: 2002,
-//     },
-// ]
-
+const cars = [
+  //? Let's look at an array of objects
+  {
+    make: 'Toyota',
+    model: 'Corolla',
+    year: 2002,
+  },
+]
 
 //* Tuples
-/*
-// let myCar = [
-//     2002,     // Year
-//     "Toyota", // Make
-//     "Corolla" // Model
-// ]
-// const [year, make, model] = myCar //✔️ Destructuring
+
+let myCar2 = [
+  2002, // Year
+  'Toyota', // Make
+  'Corolla', // Model
+]
+const [year, make, model] = myCar2 //✔️ Destructuring
 
 //? Inference doesn't work very well for tuples
-/*
-// myCar = ["Honda", 2017, "Accord", "Sedan"] //! Wrong convention
-/*
-// let myCar: [number, string, string] = [
-//     2002,
-//     "Toyota",
-//     "Corolla",
-// ]
-// myCar = ["Honda", 2017, "Accord"] //! Wrong convention
-// myCar = [2017, "Honda", "Accord", "Sedan"] //! Too many elements
 
+myCar2 = ['Honda', 2017, 'Accord', 'Sedan'] //! Wrong convention
+
+let myCar3: [number, string, string] = [2002, 'Toyota', 'Corolla']
+myCar3 = ['Honda', 2017, 'Accord'] //! Wrong convention
+myCar3 = [2017, 'Honda', 'Accord', 'Sedan'] //! Too many elements
+
+let studInfo: [string, number, boolean] = ['Alice', 12345, true]
+const [name, id, isEnrolled] = studInfo
+
+let studArr = ['Alice', 'Ankit', 'Anand'] //? Inference: string[]
+const [stud1, stud2, stud3, stud4] = studArr //! stud4 is undefined, but no error!
 
 //*  `readonly` tuples
-/*
-// const numPair: [number, number] = [4, 5]; //✔️ Valid
-// const numTriplet: [number, number, number] = [7]; //! Invalid
 
-// [101, 102, 103].length //? number[].length
-// numPair.length //? [number, number] length
+const numPair: [number, number] = [4, 5] //✔️ Valid
+const numTriplet: [number, number, number] = [7][(101, 102, 103)] //! Invalid
+  .length //? number[].length
+numPair.length //? [number, number] length
 
-// numPair.push(6) // [4, 5, 6]
-// numPair.pop() // [4, 5]
-// numPair.pop() // [4]
-// numPair.pop() // []
+numPair.push(6) // [4, 5, 6]
+numPair.pop() // [4, 5]
+numPair.pop() // [4]
+numPair.pop() // []
 
-// numPair.length  //! ❌ DANGER ❌
+numPair.length //! ❌ DANGER ❌
 
-// const roNumPair: readonly [number, number] = [4, 5]
-// roNumPair.length
-// roNumPair.push(6) // [4, 5, 6] //! Not allowed
-// roNumPair.pop() // [4, 5] //! Not allowed
+const roNumPair: readonly [number, number] = [4, 5]
+roNumPair.length
+roNumPair.push(6) // [4, 5, 6] //! Not allowed
+roNumPair.pop() // [4, 5] //! Not allowed
 
 /**/