[08-08-2022] JS

x=21
console.log(x);
let x;

function fun(a) {
    return new Promise((resolve, reject) => {
        if(a>=0) {
            resolve("Positive");
        }
        else {
            reject("Negative");
        }
    })
}
fun(10)
.then((result) => console.log(result))
.catch((error) => console.log(error))

Alternative of Promises => 
1) The keyword async before a function makes the function return a promise:
2) await makes a function wait for a Promise

async function fun(a) {
    if(a>=0) {
        return "positive";
    }
    else {
        return "negative";
    }
}
fun(-10)
.then((result) => console.log(result))
.catch((error) => console.log(error))

function fun(a) {
    return new Promise((resolve) => {
        if(a>=0) {
            resolve("Positive");
        }
    })
}
fun(-10)
.then((result) => console.log(result))
.catch((error) => console.log(error))

var prom;
async function fun(a) {
    prom = new Promise((resolve) => {
        if(a>=0) {
            setTimeout(function() { return resolve("Positive");},5000);
        }
    })
    var out = await prom;
    console.log(out);
}

fun(10);
prom.then(
    (result) => {
        console.log(result);
    })

#Adding Some Delay :

var prom;
let myPromise;
prom =  new Promise(
    function(myResolve, myReject) {
  let x = 0;

// some code (try to change x to 5)

  if (x == 0) {
    setTimeout( function () { return myResolve("OK") }, 3000);
  } else {
    myReject("Error");
  }
})

function fun(a) {
    return new Promise((resolve, reject) => {
        if(a>=0) {
            setTimeout(() => resolve("Positive"), 3000);
        }
        else {
            reject("Negative");
        }
    })
}
fun(10)
.then((result) => console.log(result))
.catch((error) => console.log(error))

prom.then(
  function(value) {console.log(value);},
  function(error) {myDisplayer(error);}
  
############################################
  
{
var/let/const interval = setInterval(myFunction, 1000);
}

(function() {clearTimeout(interval)})();

function myFunction() {
  let d = new Date();
  document.getElementById("demo").innerHTML=
  d.getHours() + ":" +
  d.getMinutes() + ":" +
  d.getSeconds();
}