await and async replace the promises?

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await and async replace the promises?

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#1 by (6 votes)

3

In the following code works async and await, my doubt is that if I use async it is no longer necessary to use promises?

async function getMain() {
  var film = 'hola mundo'
    console.log(film);
  return film
};

getMain().then(function(x){console.log(x,'hola')});

javascript

asked by hubman 08.09.2018 в 04:57

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1 answer

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score 6 · Answer 1

Answering your first question, not async and await do not replace the promises , in fact the two can coexist in the same scenario; below async and await handle promises to solve the states

On the other hand in your example that you put first should look like this

async function getMain(){
  let message = 'Hola Mundo'
  const response = await (message)
  console.log(response)
}

getMain()//aquí mando ejecutar la función

Where, as you can see after the declaration of the function with keyword async , I do:

I assign a variable message the value of "hola mundo" I want to print

after a constant I equal it with variable message but indicating that it must wait for the resolution of this same with the keyword await

later I print the value with the help of console.log()

Finally, for the function to work, I only invoke it by its name and a pair of parentheses

UPDATE

If you need to compare the same exercise but from the perspective of the explicit use of promises , I leave this example also functional

let message = new Promise(function(resolve, reject){
  let saludo = 'Hola Mundo'; 
  resolve(saludo)
})

message.then((response) => {
  console.log(response)
}).catch((error) => {
  console.log(error.message)
})

Where you can notice that to this day we have three states of the promises: resolve , pending and reject

Resolve : it is the moment that the code flow worked normal and the contained logic was executed

Pending , does not exist as such an error in the code but is waiting to return the result of the promise

Rejected : indicates that it was rejected, however unlike a trhow exception, it does not kill the code flow

With regard to the last question, if it can be the case multiple await within others; I leave an example that I have with a Exercise in VueJS and it's functional for me

getFotos: async function(){
        let data = await(await fetch("https://api.example.com/fotos")).json()
        this.datos = data
      }