您应该知道的11个JavaScript和TypeScript速记

function myFn(variable1, variable2) {
let var2 = variable2 ?? "default value"
return variable1 + var2
}
myFn("this has", " no default value") //returns "this has no default value"
myFn("this has no") //returns "this has no default value"
myFn("this has no", 0) //returns "this has no 0"

function myFn(variable1, variable2) {
  variable2 ??= "default value"
  return variable1 + var2
}


myFn("this has", " no default value") //returns "this has no default value"
myFn("this has no") //returns "this has no default value"
myFn("this has no", 0) //returns "this has no 0"

//Old way...
class Person {

  private first_name: string;
  private last_name: string;
  private age: number;
  private is_married: boolean;

  constructor(fname:string, lname:string, age:number, married:boolean) {
    this.first_name = fname;
    this.last_name = lname;
    this.age = age;
    this.is_married = married;
  }
}


//New, shorter way...
class Person {


  constructor( private first_name: string,
               private last_name: string,
               private age: number,
               private is_married: boolean){}
}

// Original IF..ELSE statement
let isOdd = ""
if(variable % 2 == 0) {
  isOdd = "yes"
} else {
  isOdd = "no"
}


//The ternary approach
let isOdd = (variable % 2 == 0) ? "yes" : "no"

let variable = true;
 
(variable) ? console.log("It's TRUE") : console.log("It's FALSE")

if( expression1 || expression2 || expression3 || expression4)

function myFn(variable1, variable2) {
  let var2 = variable2 || "default value"
  return variable1 + var2
}


myFn("this has", " no default value") //returns "this has no default value"
myFn("this has no") //returns "this has no default value"

let x = 3.8
let y = ~x //this turns x into -(3 + 1), remember, the number gets turned into an integer
let z = ~y //this turns y (which is -4) into -(-4 + 1) which is 3


//So you can do:


let flooredX = ~~x //and this performs both steps from above at the same time

let name:string = "Fernando";
let age:number = 36;
let id:number = 1;


type User = {
  name: string,
  age: number,
  id: number
}


//Old way
let myUser: User = {
  name: name,
  age: age,
  id: id
}


//new way
let myNewUser: User = {
  name,
  age,
  id
}

let myArr:number[] = [1,2,3,4,5,6,7,8,9,10]


//Long way of doing it:
let oddNumbers:number[] = myArr.filter( (n:number) => {
  return n % 2 == 0
})


let double:number[] = myArr.map( (n:number) => {
  return n * 2;
})




//Shorter way:
let oddNumbers2:number[] = myArr.filter( (n:number) => n % 2 == 0 )


let double2:number[] = myArr.map( (n:number) =>  n * 2 )

const m = _ => if(2) console.log("true")  else console.log("false")

//We can function without the last 2 parameter because a default value
//can be assigned to them
function myFunc(a, b, c = 2, d = "") {
  //your logic goes here...
}

const mandatory = _ => {
  throw new Error("This parameter is mandatory, don't ignore it!")
}




function myFunc(a, b, c = 2, d = mandatory()) {
  //your logic goes here...
}


//Works great!
myFunc(1,2,3,4)


//Throws an error
myFunc(1,2,3)

!!23 // TRUE
!!"" // FALSE
!!0 // FALSE
!!{} // TRUE

const myObj = {
  name: "Fernando",
  age: 37,
  country: "Spain"
}


//Old way of doing this:
const name = myObj.name;
const age = myObj.age;
const country = myObj.country;


//Using destructuring
const {name, age, country} = myObj;

const { get } from 'lodash'

const arr1 = [1,2,3,4]
const arr2 = [5,6,7]


const finalArr = [...arr1, ...arr2] // [1,2,3,4,5,6,7]


const partialObj1 = {
  name: "fernando"
}
const partialObj2 = {
  age:37
}


const fullObj = { ...partialObj1, ...partialObj2 } // {name: "fernando", age: 37}

const myList = [1,2,3,4,5,6,7]
const myObj = {
  name: "Fernando",
  age: 37,
  country: "Spain",
  gender: "M"
}


const [head, ...tail] = myList


const {name, age, ...others} = myObj


console.log(head) //1
console.log(tail) //[2,3,4,5,6,7]
console.log(name) //Fernando
console.log(age) //37
console.log(others) //{country: "Spain", gender: "M"}

const [...values, lastItem] = [1,2,3,4]