Understanding JS Promises

Question

I would like to get a deeper understanding of how Promises work internally. Therefore I have some sample code:

var p1          


        

Answer 1

Normally code is synchronous - one statement executes like (fileopen) and there is a guarantee that the next statement will execute immediately afterwards like filewrite()

but in asynchronous operations like nodejs, you should assume that

• you have no idea when the operation will complete.
• You can't even assume that just because you send out one request first, and another request second, that they will return in that order
• Callbacks are the standard way of handling asynchrnous code in JavaScript
• but promises are the best way to handle asynchronous code.
• This is because callbacks make error handling difficult, and lead to ugly nested code.
• which user and programmer not readble easily so promises is the way