nodeJS_Day2

Sol 1 :
As Node architecture is single-threaded and asynchronous, the community devised the callback functions, which would fire (or run) after the first function (to which the callbacks were assigned) run is completed.
app.get('/', function(){
 function1(arg1, function(){
   ...
})
});
The problem with this kind of code is that this kind of situations can cause a lot of trouble and the code can get messy when there are several functions. This situation is called what is commonly known as a callback hell.
So, to find a way out, the idea of Promises and function chaining was introduced.

Example: Before async/await
function fun1(req, res){
  return request.get('http://localhost:3000')
   .catch((err) =>{
     console.log('found error');
}).then((res) =>{
   console.log('get request returned.');
});

With Node v8, the async/await feature was officially rolled out by the Node to deal with Promises and function chaining. 

Example :
async function fun1(req, res){
  let response = await request.get('http://localhost:3000');
    if (response.err) { console.log('error');}
    else { console.log('fetched response');
}

Sol 2 :
var words = [ 'Laptop','bus' , 'Parking', 13 ,'453']; 
words.map(w=>w.length);