understanding promise and async function using example

working link->https://stackblitz.com/edit/js-it5ura?file=index.js

//passing value to a promise using arrow function

let numberSlover=(x)=>new Promise((resolve, reject)=>{

if(typeof x=="number")

{

resolve("Pass")

}else

{

reject("Fail")

}

})

numberSlover(22).then((data)=>

{

console.log(data);

},(data)=>{

console.log(data);

}

)

//now even better than above using async function which return a promise

async function add(op,one,two)

{

let result;

if(op==="+")

{

result=one+two;

}else if(op==="/")

{

result=one/two;

}else if(op==="*")

{

result=one*two;

}else if(op==="-")

{

result=Math.max(one,two)-Math.min(one,two);

}

return result;

}

add("+",100,200).then(

(data)=>{

console.log(data);

}

)

add("-",100,9200).then(

(data)=>{

console.log(data);

}

)

Passing parameter to a promise using arrow function

//passing value to a promise using arrow function

let numberSlover=(x)=>new Promise((resolve, reject)=>{

if(typeof x=="number")

{

resolve("Pass")

}else

{

reject("Fail")

}

})

numberSlover(22).then((data)=>

{

console.log(data);

},(data)=>{

console.log(data);

}

)

type aliases implementing your own type in typescript

 type aliases or our your own type is one of the most important part of typescript see how you can implement type aliases in typescript using type .

link->https://stackblitz.com/edit/typescript-7barjt

//creating your own type or type alias in typescript is very easy for example

//direction type what only allowed dirction values

export type Direction="north"|"south"|"east"|"west";

//strArray allowed only string and array where array is number of boolean type

export type strArray=string|Array<number|boolean>;

//an interfacce type---------

export type userdd=userDD;

interface userDD

{

userDirection:Direction

username:string

}

class human

{

private direction:Direction;

private myarray:strArray;

private newuser:userdd;

constructor()

{

/*

myarray is string and array type where Array is number or boolean

type so any other value in myarray not allowed

*/

//not allowed

//this.myarray=["manish"]

//allowrd

this.myarray=[true,false];

//newuser is userDD type so both below value allowed because

username is string type and userDirection is direction type

this.newuser={

username:"manish",

userDirection:"east"

}

}

public setDirection(_direction:Direction)

{

this.direction=_direction;

}

public getDirection()

{

return this.direction;

}

public moveMe()

{

switch(this.direction)

{

case "north":

console.log("move north")

break;

case "south":

console.log("move south")

break;

case "east":

console.log("move east")

break;

case "west":

console.log("move west")

break;

}

}

}

//check your type

var h=new human();

h.setDirection("north")//move human to north direction

h.moveMe();

how to create a very simple calculator using reactjs and typescript

https://stackblitz.com/edit/react-ts-pxyzyh  calculator  is not completed is a just a basic idea how to can create a simple calculator in reactjs