Why are these sampling methods asynchronous?

Question

Fetch is the new Promise-based API for creating network requests:

fetch('https://www.everythingisawesome.com/')
  .then(response => console.log('status: ', response.status));

It makes sense to me - when we initiate a network call, we return Promise, which allows our thread to continue working with another business. When an answer is available, the code inside Promise is executed.

However, if I am interested in the response payload, I do this using the response methods, not the properties:

• ArrayBuffer ()
• blob ()
• FormData ()
• JSON ()
• text()

These methods return promises, and I don't understand why.

fetch('https://www.everythingisawesome.com/') //IO bound
  .then(response => response.json()); //We now have the response, so this operation is CPU bound - isn't it?
  .then(entity => console.log(entity.name));

Why handling the response payload returns a promise - I don’t understand why this should be an async operation.

Answer 1

Why are these sampling methods asynchronous?

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• arrayBuffer() ArrayBuffer.
• blob() Blob.
• formData() FormData.
• json(), , JSON.
• text() .

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Answer 2

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Answer 3

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fetch('https://www.everythingisawesome.com/')
  .then(function(response) {
    return response.json()
  })
  .then(function(json) {
    console.log('parsed json', json)
  })
  .catch(function(ex) {
    console.log('parsing or loading failed', ex)
  })

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Answer 4

, promises . -, json() FileReader . FileReaders onload, .

function fileReaderReady(reader) {
  return new Promise(function(resolve, reject) {
    reader.onload = function() {
      resolve(reader.result)
    }
    reader.onerror = function() {
      reject(reader.error)
    }
  })
}

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