CODEWITHSUNDEEP
javascriptpromise
suedar
suedar

Reputation: 130

A ques about promise

I just read a article about promise. And I am really confused.

Why is 

const bookPromise = bookModel.fetchAll();
const authorPromise = authorModel.fetch(authorId);
const book = await bookPromise;
const author = await authorPromise;

is a better way than 

const books = await bookModel.fetchAll();
const author = await authorModel.fetch(authorId);

The author explained that it make the promise serial execution. But i justcan not see the difference. Can you explain about this to me. Thx.

Upvotes: 2

Views: 46

Answers (1)

CertainPerformance
CertainPerformance

Reputation: 370729

In the first snippet, both Promises are declared, and the asynchronous code for both starts running immediately - both network requests (or whatever the operation is) gets sent out immediately. In the second snippet, the author Promise does not start until the books Promise has resolved - if latency is high, for example, that could be a problem. Better to send out both requests at once, rather than requiring one to be completed before starting the other one.

It might be clearer to use Promise.all instead, though:

const [book, author] = await Promise.all([
  bookModel.fetchAll(),
  authorModel.fetch(authorId)
]);

Upvotes: 3

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