week 9.3, enum, generics, import, export, typescript.

//enum is another cleaner way to write  constant value

enum direction {
Up,
Down,
Left,
Right
}

doSommthing(direction.up) 

const app = express();

enum ResponseStatus{

    Success = 200,

    NotFond = 404,

    Error = 500

}

//200, 404,  500

app.get("/", (res, res) => {

    if (!req.query.userId) {

        res.status{ResponseStatus.NotFond}

    }

    //and so on

    res.json({});

})

app.get("/", (res, res) => {

    if (!req.query.userId) {

        res.status{ResponseStatus.NotFond}

    }

    //and so on

    res.json({});

})

//Generic

// User can send different type of values in inputs, without any type errors.

// Typescript isn't able to infer the right type of the return type

// User can send different type of values in inputs, without any type errors.

// Typescript isn't able to infer the right type of the return type

// ugly

type Input = number | string;

//200, 404,  500

function firstEl(arr:Input[]) {

    return arr[0];

}

const value = firstEl([1,2,3, "dhrup"])

//-------------------------

//pretty

//<T> represent any thing value is pass on the parameter.

//it is a generics

function identity<T>(arg: T) {

    return arg;

}

let output1 = identity("myString");

let output2 = identity(100);

 

//----------------------- 

function getFirstElement<T>(arr: T[]) {

    return arr[];

}

var output1 = getFirstElement(["harkiratSingh", "dhrupSinha"]);

var output2 = getFirstElement([100,30]);

console.log(output1.toLowerCase());

 

//importing in TS

import express from "express";

//exporting in TS

export default a;

export const a = 1;