JAVASCRIPT

what is synchronous and asynchronous in javascript

Synchronous:
- In synchronous operations tasks are performed one at a time and only when one 
is completed, the following is unblocked. In other words, you need to wait for a
task to finish to move to the next one.

Asynchronous:
- In asynchronous operations, you can move to another task 
before the previous one finishes.

what is synchronous and asynchronous in javascript

Synchronous: In synchronous operations tasks are performed one at a time and only when one 
is completed, the following is unblocked. In other words, you need to wait for a
task to finish to move to the next one.

function getUsername(callback) {
    setTimeout(() => {
        console.log("Alextz")
        callback()
    }, 2000)
}

getUsername(() => console.log("getUsername callback called"))

Asynchronous:  In asynchronous operations, you can move to another task 
before the previous one finishes.


function getUser(callback) {
    setTimeout(() => {
        console.log("Alextz")
    }, 2000)

    // get executed even though the user has not printed yet
    callback()
}

getUser(() => console.log("getUser callback called"))

js use await in synchronous method

var btn = document.getElementById("btn");

btn.addEventListener("click", handler, false);

function handler(e) {
  console.log("handler triggered");
  doSomething();
  console.log("handler done");
}

function doSomething() {
  doThis();
  doThat();
  doTheOther();
}

function doThis() {
  console.log("doThis - start & end");
}
function doThat() {
  console.log("doThat - start");
  // do something that takes a while
  var stop = Date.now() + 1000;
  while (Date.now() < stop) {
    // wait
  }
  console.log("doThat - end");
}
function doTheOther() {
  console.log("doThat - start & end");
}